The final race of the World Challenge weekend at Sonoma, Round 19 for GT and Round 17 for GTA and GT Cup, saw Renger van der Zande take the overall win with Frankie Montecalvo and Colin Thompson winning in their respective classes.

From the standing start, van der Zande, having started second on the grid in the No. 31 EFFORT Racing Porsche 911 GT3R, passed polesitter Robert Thorne of the No. 6 K-PAX Racing 650S GT3 for the early lead. Thorne's teammate and winner of Saturday's Round 18, Kevin Estre of the No. 9 K-PAX McLaren, slotted into third.

As the field snaked through Turn 2, a number of cars collided, bringing out a full-course caution and ending the day for a handful. Retiring from the race due to the incident were Mike Skeen in the No. 41 CRP Racing Audi R8 LMW Ultra, Peter Cunningham in the No. 41 RealTime Racing Acura TLX-GT, Chris Dyson in the No. 16 Bentley Team Dyson Racing Bentley Continental GT3 and Michael Lewis of the No. 41 EFFORT Porsche 911 GT3R.

Launching cleanly into the lead in the GTA class was points leader Montecalvo in the No. 66 DragonSpeed Mercedes-Benz AMG SLS GT3. Due to the incident at Turn 2 ahead of them, the GT Cup class race began under yellow with polesitter and points leader Thompson assuming the lead in the No. 11 Porsche of Bucks County Porsche 911 GT3 Cup.

The restart came on Lap 4 and saw van der Zande lead the field to and through Turn 1 with the K-PAX McLarens of Thorne and Estre going side-by-side through Turns 2 and 3; Estre completed the pass on his teammate and advanced into third.

In GTA, Montecalvo remained at the front with Eric Lux, driver of the No. 08 DragonSpeed Mercedes-Benz and Henrique Cisneros of the No. 30 MOMO NGT Motorsport Ferrari 458 GT3 Italia in second and third, respectively, in class.

Thompson led GT Cup Round 16 winner Alec Udell of the No. 17 Global Motorsports Group car and Sloan Urry of the No. 02 TruSpeed Autosport entry.

By Lap 7, van der Zande had pulled 0.819-seconds ahead of Estre, increasing his lead slightly through Lap 10. In GTA, Montecalvo remained at the front with Lux behind him while Martin Fuentes of the No. 07 Scuderia Corsa Ferrari moved into third after Cisneros who had previously been in third was issued a drive through penalty for contact during the standing start.

On Lap 12, Andy Pilgrim, at the wheel of the No. 8 Cadillac Racing Cadillac ATS-VR GT3 closed in on Beretta - but he was never able to make the pass. Up front, van der Zande and Estre disappeared from the rest of the field.

At the checkers, van der Zande took his first career World Challenge win ahead of Estre and Beretta. Thorne and Pilgrim battled furiously on the final lap, with Pilgrim getting by Thorne in Turn 7 only to have Thorne pass again as they came to the checkers.

In GTA, Montecalvo scored his seventh win of the season over Lux and Fuentes, while Thompson won his 12th race of 2015 with Udell and Urry rounding out the GT Cup podium behind him.

Leaving Sonoma, O'Connell remains in the lead of the Drivers' Championship points while Montecalvo and Thompson lead in GTA and GT Cup.

Next up for these three classes is the 2015 season finale, set for the weekend of September 11-13 at Mazda Raceway Laguna Seca.

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Aaron Durant is the editor of the VAVEL USA Racing section. Follow him on Twitter at @DoubleA291.