Fernando Alonso believes the braking problem that dropped his United Autosports Ligier 26 laps off the lead has cost his team a possible top-five result.
The #23 car had been running as high as sixth, with Alonso claiming they were "in contention" for a top-five finish.
A puncture sustained during team-mate Phil Hanson's stint followed by Alonso suffering a brake problem combined to drop them 26 laps behind the leaders.
Despite failing to stop for Turn 1 and cutting across the infield when the brakes failed, Alonso did return the Ligier to the pits.
While the car has emerged again after having a brake master cylinder replaced, the United Autosports car has dropped to 15th in class and 22nd overall with third driver Lando Norris 26 laps down.
After the incident, Alonso explained on Instagram: "Unlucky situation with Phil; we had a puncture just before I jumped in the car.
"We lost four laps there with some damage on the car.
"But my stints were good. We had a little bit of pace at night, the car felt much better.
"Also we had the safety car and managed to recover two laps, so we were in contention for the top five probably. We were P6 already.
"And we had a brake issue and we had to put the car in the garage.
"Obviously the positions are compromised, we are losing a lot of laps, so that's a shame.
"We will try our best until the last lap."
Penske led the race at the halfway mark after its Acura overhauled the Action Express Cadillac.
The other United Autosports car, in the hands of ex-Formula 1 driver Paul di Resta, was up to sixth.