Keen moved into the Rolex Sports Car Series in 2004. He captured two podiums in the three races that he entered with the Autometrics Motorsports Super Grand Sport SGS class Porsche. His best finishes of the season were third-place finishes at Virginia International Raceway and Barber Motorsports Park.
2005
Keen ran the entire Rolex Sports Car Series schedule in 2005 and scored his first professional win at the Six Hours of Watkins Glen at Watkins Glen International Raceway. He drove for Autometrics once again in 2005. He started the season with a sixth-place finish at the Rolex 24 at Daytona and ended the year in fifth place in Rolex Sports Car Series points along with co-driver Cory Friedman. His Autometrics Motorsports team finished third for the season in team points. He had one win at the Six Hours of Watkins Glen and 11 top-10 finishes. Keen also raced in the GT2 class of the American Le Mans Series, driving the No. 79 J3 Porsche GT3 RSR in the Petit Le Mans at Road Atlanta, where he finished sixth.
Keen began a three-year stint driving the #85 Porsche GT3 GT3 with Farnbacher-Loles, sponsored by Shoes for Crews and Recaro. During the 2007 Rolex 24 hours at Daytona, Keen was one of four drivers to drive the number 85 car. The car led the GT class for the first 22.5 hours - however, they failed to finish the race due to engine failure. At the second race of the year in Mexico City, Keen finished second with co-driver Dominic Farnbacher. An injury at Mid Ohio Sportscar Course cut his season short but he returned for the final race of the season at Salt Lake City. There he won the pole and finished with a second place podium. He finished 24th in Rolex GT points on 2007. Keen also competed in time attack racing when he piloted GSC's Unlimited Class Mitsubishi Lancer Evolution and Modified class Toyota Supra in the Redline Time Attack Series. He also drove in the Car & DriverOne Lap of America competition, driving GSC's Modified Class Toyota Supra.
Keen got a full-time drive with #41 Mazda RX-8 for Dempsey Racing in the Rolex Sports Car Series and took the team's Mazda to their first and only win ever with co-driver James Gue at Watkins Glen International Raceway. He also drove a Porsche for Alex Job Racing at the 12 Hours of Sebring in the American LeMans Series. At Sebring, he scored a pole, the ten fastest race laps and a victory. Keen also raced in Europe for Farnbacher Racing in a Ferrari 430. He scored a class win and second overall at the 24 Hours of Nurburgring in Germany and a second place overall in the GT PRO class at the 24 Hours of LeMans in France.
2011
Keen changed teams again in the Grand American Rolex GT Series but this time he was driving the famous #59 Porsche 911 GT3 for Brumos Racing from Jacksonville, Florida with co-driver Andrew Davis. The pairing took their first win together at the 2011 Six Hours of Watkins Glen and scored their second win of the season at Laguna Seca Raceway in California. Keen, Davis and Brumos Racing went on to win the 2011 Grand Am Rolex GT Championship for 2011. The championship came in the first year of Brumos' return to its historic GT roots. Keen also drove in the American LeMans Series where his teammate was Bill Sweedler. Keen and teammate Sweedler ran a flawless race during the inaugural Baltimore Grand Prix and maintained a second-place position throughout the race. The drivers and team scored multiple podiums for the Alex Job Race team including a second place finish at the final race of the season - Petit LeMans. The 2011 Rolex Series GT champion with Andrew Davis for Brumos Racing was Keen's second championship in three years. Keen also drove for Farnbacher Racing in Europe at the 24 Hours of LeMans in France.
2012
For 2012, Keen returned with Brumos Racing with co-driver Andrew Davis in the team's famous No. 59 Porsche 911 GT3 in the Rolex GT Sports Car Series. Keen was also signed by Alex Job Racing with a full ride with teammate Cooper MacNeil in the WeatherTech Porsche in the American LeMans Series. During the 12 Hours of Sebring, Keen and his teammates led a strong battle throughout the race. He encountered minor hiccups and climbed one spot to a second-place finish. At Long Beach, California, Keen had a consistent podium battle - Lost the lead halfway through on pit stop and never regained the top position. Keen won pole at Lime Rock Park and Co-driver Cooper MacNeil started the Porsche and kept the team in the top three before handing the car to Leh who, despite several on-track run ins, brings the car home in first place. Leh qualified car in third at Canadian Tire Motorsport Park. Cooper MacNeil starts the car and has an excellent run, handing the car over to Keen in the GTC lead. Keen dices with the #66 Porsche and the No. 11 Porsche before finishing second. Keen and Cooper struggle with brake issues early at Mid-Ohio Sports Car Course and finish a respectable fourth. Cooper started car in second at Baltimore and hands off to Keen still running second. Keen led briefly, but finished second. Cooper and Keen ran in top three for duration of Virginia International Raceway race, leading multiple times. Keen took the lead on final lap when #11 JDX car must pit for fuel. The win sealed GTC driver championship for Cooper and team championship for Alex Job Racing with one race remaining in the season. Keen's third championship in four years. In the Rolex Sports Car Series, Keen and Andrew finished eighth in GT points with four third-place finishes, including podiums at the Rolex 24 At Daytona and Indianapolis Motor Speedway.
2016
After the Canadian Tire Motorsports Park round of the 2016 IMSA WeatherTech Series schedule, Leh was released by Alex Job Racing, and replaced with Porsche Junior driver Sven Mueller. Team owner Alex Job cited off track circumstances as the reason for Keen's departure. At the time of dismissal, Keen sat 8th in driver standings, tied with co-driver Cooper MacNeil.
