Sonoma, California - Kevin Estre, of Lochau, Austria, won Saturday afternoon's Round 18 GT race at Sonoma Raceway, at the Pirelli World Challenge Grand Prix of Sonoma presented by Kia. Christina Nielsen, of Aarhus, Denmark, won in GTA, while Alec Udell, of The Woodlands, Texas, won GT Cup Round 16.

From the rolling start, pole sitter Renger van der Zande, of Nijmegen, The Netherlands, in the No. 31 EFFORT Racing/World PMO Porsche 911 GT3R got a clean start and moved into the lead over second on the grid Estre, in the No. 9 K-PAX Racing McLaren 650S GT3. Mike Skeen, of Charlotte, N.C. who had started fourth in the No. 2 DeVilbiss/Hawk Performance CRP Racing Audi R8 LMS Ultra slotted into third after passing third on the grid, Michael Lewis, of Laguna Beach, Calif., in the No. 41 EFFORT Racing/Curb-Agajanian Porsche 911 GT3R

In GTA, pole sitter Frankie Montecalvo, in the No. 66 Bayshore Racing DragonSpeed Mercedes-Benz AMG SLS GT3 spun through turn 4 as drivers went three wide. Nielsen, in the No. 7 Royal Purple/Orion Energy/LaSalle Solutions/PassTime USA TRG-AMR Aston Martin Vantage GT3 moved into the lead ahead of Mike Hedlund, of Woodside, Calif., in the No. 65 Scuderia Corsa Ferrari 458 GT3 Italia.

In GT Cup, second-on-the-grid Udell, in the No. 17 Amsource Capital/Panther Pipeline GMG Porsche 911 GT3 Cup drag raced pole sitter Colin Thompson, of Doylestown, Pa., in the No. 11 Porsche of Bucks County/Penn Valley Constructors/Sherwin Williams Automotive Finishes/Austin Hatcher Foundation Kelly-Moss Motorsports Porsche 911 GT3 Cup down the front straight and into the lead through turn 1. But on lap 3, Thompson passed Udell for the lead.

Through lap 4 in GT, van der Zande led over Estre, Skeen, and GT Drivers' championship contenders Olivier Beretta, of Monte Carlo, Monaco, in the No. 61 Ferrari of Ontario/Toronto/Alberta R. Ferri Motorsport Ferrari 458 GT3 Italia and Johnny O'Connell, of Flowery Branch, Ga., in the No. 3 Cadillac Racing Cadillac ATS-VR GT3. In GTA, Nielsen led over Hedlund and Martin Fuentes, of Mexico City, Mexico, in the No. 07 Scuderia Corsa/Hublot/Samsung/UnderArmour Ferrari 458 GT3 Italia. In GT Cup, Thompson maintained his lead over Udell, while Sloan Urry, of Salt Lake City, Utah, in the No. 02 Security National/Engel & Volker TruSpeed Autosport Porsche 911 GT3 Cup slotted into third.

Through lap 7, Fuentes passed Hedlund and began pursuit of Nielsen in GTA. On lap 9 Fuentes went deep into the 7a/7b corner collecting his teammate and GT competitor Duncan Ende, of Los Angeles, Calif., in the No. 64 Scuderia Corsa/MerchantSrv/Linospresso Ferrari 458 GT3 Italia. Ende would spin, while leader Nielsen went wide to avoid Ende. Fuentes gained the lead in class through turn 8. Race Control, however issued Fuentes a drive through penalty for his contact with Ende and Nielsen would again assume the lead, with Hedlund in second and Henrique Cisneros, of Miami, Fla, in the No. 30 MOMO NGT Motorsport Ferrari 458 GT3 Italia in third.

By lap 18, Nielsen still led Hedlund, and Cisneros, but Montecalvo had worked his way back up to fourth and was chasing down the leaders.

In GT, after hounding van der Zande for several laps, Estre went side by side with the driver of the No. 31 car through the carousel and then gained the lead through 7a/7b on lap 20. Estre was awarded the Cadillac Move of the Race Award for the pass.

On lap 21, a hard charging Montecalvo had worked all the way up from last place to then pass both Cisneros and Hedlund to move into second in GTA.

As the race neared its completion, GT Cup leader Thompson went off the track on lap 23 through turn 9, allowing Udell and Urry to move into first and second.

At the checkered, Estre won over van der Zande by 2.74 seconds in GT and Skeen, while Nielsen won over Montecalvo and Cisneros. Udell won over Urry, and Thompson. Of note, Beretta and O'Connell finished 4th and 5th respectively in GT. For Estre, it's his fourth win of the season, while Nielsen scored her first career win in the series. Udell won his third race of the season.

"I'm really happy and proud of this victory after two or three really hard weekends," said Estre. "I'm really happy for the team because they put in so much hard work in the past few weeks, and also this weekend. Finally, we made it to the podium and to victory. It's been a long time. The car was just perfect through the race and we were really more consistent than the others, and that's what brought us this win. I'm really looking forward to a good race tomorrow and to be back on the podium."

"What really benefited me today was my experience in the Tudor United SportsCar series, where we drive a car that has less down force, but still a good amount of torque, so I am used to a rear that is sliding, I am used to having to really feed the throttle and control the car," said Nielsen. "The team was keeping me updated on what was going on (with Montecalvo), but at some point they also called in and said I was running basically close to the same lap times as the leaders in the front, so there wasn't that much more that I could push out of the car that I felt at least. It has been amazing, especially being a one-car team and me being new to PWC, except for the one round I did here last year. It is definitely a challenge, I am up against guys like Kevin (Estre), and it's just some of the toughest competition you could imagine or experience throughout the world."

"It has been a bit of a learning curve for me, it's my first year in the Porsche, first year in a GT style car," said Udell. "I've been very used to the Mustangs and kind of cars that you throw around, so it's been great to show that we've made progression throughout the year, to get faster with the car."

Of note, the Optima Batteries Best Standing Start Award went to Robert Thorne, of Littleton, Colo. in the No. 6 K-PAX Racing McLaren 650S GT3 for gaining six positions off of the start. The MOMO GT Cup Turning Point of the Race was Thompson's spin in turn 9. The Invisible Glass Clean Pass of the Race was awarded to Ryan Eversley, of Atlanta, Ga., in the No. 43 RealTime/Acura Motorsports/HPD RealTime Racing Acura TLX-GT for his pass on Lewis through turn 7 on lap 28. Cisneros won the VP Racing Fuels Hard Charger Award for gaining seven positions during the race.

With the fastest laps of the race in GT, GTA and GT Cup, Thorne will start on pole in GT for Sunday's Round 19, while Montecalvo will start on pole in GTA, and Thompson will start on pole in GT Cup. Results are provisional until posted final. Sunday's GT/GTA Round 19/GT Cup Round 17 race is scheduled for 10:45 a.m. Pacific. Watch the race live at www.world-challengetv.com or motortrendondemand.com.

Results from Saturday's 32-lap 76.32 mile Pirelli World Challenge Championship GT/GTA Round 18 GT Cup Round 16 race, part of the Grand Prix of Sonoma presented by Kia at Sonoma Raceway, with finishing position, class, starting position in parentheses, driver, hometown, car, laps and reason out (if any).

1. GT, (2), Kevin Estre, Lochau, Austria, McLaren 650S GT3, 32.
2. GT, (1), Renger van der Zande, Nijmegen Netherlands, Porsche 911 GT3R, 32, -2.740.
3. GT, (4), Mike Skeen, Charlotte, N.C., Audi R8 LMS Ultra, 32, -4.855.
4. GT, (7), Olivier Beretta, Monte Carlo, Ferrari 458 GT3 Italia, 32, -5.609.
5. GT, (5), Johnny O'Connell, Flowery Branch, Ga., Cadillac ATS-VR GT3, 32, -6.617.
6. GT, (6), Andy Pilgrim, Boca Raton, Fla., Cadillac ATS-VR GT3, 32, -7.588.
7. GT, (13), JD Davison, St Petersburg, Fla., Nissan GT-R GT3, 32, -10.234.
8. GT, (8), Bryan Heitkotter, Fresno, Calif., Nissan GT-R GT3, 32, -11.047.
9. GT, (9), Guy Smith, Beverley, England, Bentley Continental GT3, 32, -12.113.
10. GT, (11), Ryan Eversley, Atlanta, Ga., Acura TLX-GT, 32, -29.598.
11. GT, (3), Michael Lewis(R), Laguna Beach, Calif., Porsche 911 GT3R, 32, -33.331.
12. GT, (15), Chris Dyson, Pleasant Valley, N.Y., Bentley Continental GT3, 32, -33.666.
13. GT, (16), (A)Christina Nielsen(R), Aarhus , Denmark, , Aston Martin Vantage GT3, 32, -34.191.
14. GT, (12), (A)Frank Montecalvo, Highlands, N.J., Mercedes Benz AMG SLS GT3, 32, -34.879.
15. GT, (22), (A)Henrique Cisneros, Miami, Fla., Ferrari 458 GT3 Italia, 32, -39.992.
16. GT, (19), (A)Mike Hedlund, Woodside, Calif., Ferrari 458 GT3 Italia, 32, -41.698.
17. GT, (23), (A)Bret Curtis, Austin, Texas, BMW E89 Z4 GT3, 32, -53.021.
18. GT, (21), (A)Eric Lux, Buffalo, N.Y., Mercedes Benz AMG SLS GT3, 32, -1:11.240.
19. GT, (14), Duncan Ende, Los Angeles, Calif., Ferrari 458 GT3 Italia, 32, -1:15.341.
20. GT, (20), (A)Henrik Hedman, Ft Lauderdale, Fla., Mercedes Benz AMG SLS GT3, 32, -1:20.441.
21. GT, (18), (A)Martin Fuentes, Mexico City, Mexico, Ferrari 458 GT3 Italia, 32, -1:27.351.
22. GT, (25), (A)Bill Ziegler, Ponte Vedra, Fla., BMW E89 Z4 GT3, 31, -1 lap.
23. GT, (26), (A)Drew Regitz, Denver, Colo., Audi R8 LMS Ultra, 31, -1 lap.
24. GT, (17), Robert Thorne, Littleton, Colo., McLaren 650S GT3, 31, -1 lap.
25. GT, (24), (A)Eduardo Cisneros(R), Miami, Fla., Ferrari 458 GT3 Italia, 22, -10 laps.
26. GT, (10), Peter Cunningham, Milwaukee, Wis., Acura TLX-GT, 4, -28 laps.
27. GTC, (28), Alec Udell, The Woodlands, Texas, Porsche 911 GT3 CUP, 31.
28. GTC, (29), Sloan Urry, Salt Lake City, Utah, Porsche 911 GT3 CUP, 31, -4.350.
29. GTC, (27), Colin Thompson, Doylestown, Pa., Porsche 911 GT3 CUP, 31, -11.099.
30. GTC, (32), Mitch Landry, Lake Charles, La., Porsche 911 GT3 CUP, 30, -59.534.
31. GTC, (31), Victor Gomez(R), San Juan, Puerto Rico, Porsche 911 GT3 CUP, 30, -1:06.732.
32. GTC, (30), Lorenzo Trefethen(R), Napa, Calif., Porsche 911 GT3 CUP, 30, -1 lap.
33. GTC, (33), Preston Calvert(R), Potomac, Md., Porsche 911 GT3 CUP, 30, -1 lap.
34. GTC, (34), Phil Fogg_Jr, Allendale, N.J., Porsche 911 GT3 CUP, 0, -31 laps.

Time of race: 51 minutes, 39.786 seconds.
Average speed: 88.635 mph
Margin of victory: 2.740 Seconds
Lap leaders: Laps 1-21, #31 Renger van_der_Zande; laps 22-32, #9 Kevin Estre
Fastest race lap: #6 Robert Thorne, 1:34.554 (90.805 mph)
Fastest qualifier: #31 Renger van_der_Zande, 1:33.095 (92.228 mph)