The #5 Cadillac DPi-V.R shared by Westbrook, Tristan Vautier and Loic Duval finished a close second at the Florida airfield track, losing out to the Chip Ganassi Racing Cadillac of Earl Bamber, Alex Lynn and Neel Jani by just over six seconds.
Westbrook took advantage of a drive-through penalty for Bamber in the #02 Ganassi car late in the penultimate hour to move into the lead, but the New Zealander appeared to have a pace advantage and soon repassed.
After Bamber spun following contact with a GTD car, explaining afterwards he had “made a meal” of his run to victory, Westbrook led once more until Bamber passed for good when the Briton was baulked by traffic.
Westbrook explained that its efforts were impacted by a cooling problem that required JDC to perform driver changes in each of its final three pitstops, with Vautier handing over to Westbrook for the penultimate stint before the former took over again for the run to the flag.
Bamber on the other hand was able to stay at the wheel of the #02 car for a closing triple-stint.
"All you can ask is for us to be in the hunt," said Westbrook, who moves to the head of the standings following the team's third-place finish in the season-opening Daytona 24 Hours in January.
"We were in the hunt for the whole 12 hours. We had some issues with the cooling in the car, so we could only single stint at the end.
"I found myself in the lead with an hour to go and I got [held up] by a GTD car in Turn 16. Do I try to overtake him on the outside in Turn 16?
"Second is really a good result. We’ve won a podium in both races [so far in 2022]. Everyone should be proud. Great day for Cadillac and a great day for JDC.”
While Vautier was able to close the gap to Bamber in the final stint, he was never able to get within striking distance of the #02 Ganassi machine.
"We gave it a good go," said the French driver, who won the race last year with Duval and Sebastien Bourdais. "Man, I drove my heart out in the last stint. I thought I had him [Bamber] for a while, but [we had] a couple of bad breaks catching GT cars in Turns 3, 4 and 5. We had the pace.
"I think we can be proud of what we achieved, we’re the smallest team here [and had] two amazing races at Daytona and Sebring.
"The team did an amazing job again, and just thankful to Cadillac and JDC-Miller Motorsports. I feels good to know I left it all on the racetrack."
AXR team left to rue lack of late caution
Completing an all-Cadillac top three was the #31 Whelen Engineering-branded Action Express Racing car shared by Pipo Derani, Tristan Nunez and Mike Conway, 14 seconds down at the chequered flag.
That was despite three-time Sebring 12 Hours winner Derani making contact with the #60 Meyer Shank Racing Acura of Stoffel Vandoorne and spinning during their battle for third, which temporarily dropped the #31 car to fifth.
With the race going caution-free for the final four-and-a-half hours, there was no way for Derani to catch the leading Cadillacs after he took over from team-mate Nunez for the final stint.
“It was a tough day at the office, but it was a good points day," said Derani. "Unfortunately, we couldn’t win. We didn’t get a yellow at the end so we could try to catch the front runners."
AXR's Ally Racing-branded Michelin Endurance Cup-only entry driven by Mike Rockenfeller, Kamui Kobayashi and Jose Maria Lopez ended up a distant sixth following a late brake problem.
