AJ Allmendinger was quickest in Michael Shank Racing's #60 Riley-Ford on day one of testing for the 2013 Daytona 24 Hours.
Allmendinger teamed up with Justin Wilson, John Pew and Ozz Negri to score MSR's first Daytona win in last year's event.
The NASCAR regular's best time of 1m42.918s edged out Ganassi's Memo Rojas and Dario Franchitti in a top three covered by 0.069 seconds.
Marcos Ambrose also had a run in the pacesetting MSR car. The Australian was standing in for Negri while he recovers from a training injury. It is not yet clear if NASCAR race-winner and former V8 Supercars champion Ambrose will be part of the team's line-up for the 24-hour race on 26-27 January.
MSR's second car was fourth in the hands of Michael Valiante. Starworks' #2 Riley-Ford, shared between Sebastien Bourdais, Ryan Dalziel, Allan McNish and Alex Popow, completed the top five.
The morning session had been affected by rain. Times were of little relevance as most waited for the weather to improve, but 2010 Daytona 500 winner Jamie McMurray was quickest in Ganassi's #1 car by 1.3s.
Andy Lally set the GT pace in Magnus' #44 Porsche.
Testing continues on Saturday with four further sessions including night practice.
Between test sessions on Friday, organisers of Grand-Am and the American Le Mans Series confirmed the class structure for their merged 2014 championship, with Daytona Prototypes and LMP2 equalising to form the headline category.