Luhr became series career leader in victories with 43, and he and Graf are the first drivers to repeat at Mazda Raceway Laguna Seca since 2007.
Luhr took advantage of a daring move at the downhill Corkscrew in his No. 6 Honda Performance Development ARX-03a and a late-race puncture for Rebellion Racing's Neel Jani to win the American Le Mans Monterey.
Luhr won by 6.352 seconds thanks to a late-race caution and a one-lap dash to the finish.
Corvette Racing's Jan Magnussen and Antonio Garcia won a close GT race, with the first five cars finishing within 3 seconds. The No. 3 Corvette C6 ZR1 led for the final 3 hours, 15 minutes but its lead was never more than 5 seconds.
PR1/Mathiasen Motorsports won for the second time in three races in the Prototype Challenge class presented by Continental Tire. Luis Diaz got around CORE autosport's Colin Braun on the final restart in the No. 52 ORECA FLM09 he drove with Michael Guasch.
Nick Tandy passed Andy Lally near the halfway point of the final lap to win GT Challenge for NGT Motorsport. Tandy, who drove with Henrique Cisneros in the No. 30 Porsche 911 GT3 Cup was three seconds behind Lally at the restart. NGT won for the second race in a row.
Lally was looking to give co-driver and team owner Patrick Dempsey his first major sports car race victory.
Marino Franchitti and Scott Tucker led a 1-2 finish for Level 5 Motorsports in P2. Their No. 551 HPD ARX-03b was 5.578 seconds ahead of the No. 552 sister car, which Tucker drove with Ryan Briscoe.