Reliability issues have plagued the McLaren Honda team all weekend, the result of which was a disappointing race day at the United States Grand Prix that finished outside the points.
This morning the team identified an issue with Stoffel's MGU-H, but without sufficient time to change that element before the pit lane opened, the decision was made to change entire power unit. This inflicted a further 25-place grid penalty on his starting position in addition to the original five-place drop for changing the ICE on Friday morning.
Starting from the back, Stoffel made a great start, gaining three places on the first lap, and began to make good progress through the field. He put up an impressive fight on a track that he'd never raced on before, overtaking [Marcus] Ericsson, [Kevin] Magnussen, [Romain] Grosjean and [Lance] Stroll (who later re-passed him on the final lap). Despite a valiant effort, he finished in 12th position just outside the points and with little reward for the difficulties faced here since Friday.
Although Fernando didn't incur any penalties before the race started, he too wasn't exempt from reliability issues. Like Stoffel, he made a strong start, protecting the gap to the cars around him and showing solid pace up to and through the first round of pit stops. Unfortunately, on lap 24 while running in eighth place (a net seventh as [Felipe] Massa hadn't pitted), he lost power - later diagnosed as an MGU-H problem - and was forced to retire the car.
Fernando Alonso: "Today I think we really deserved to collect some points. We did a good qualifying, a good race, and made a good start, but with no reward. From our side I think it was an amazing performance.
"On the straight I lost power - I felt some vibrations in the engine and some really weird things were going on. It's such a pity. In the last few races we have lost so many points - possibly 15 or 20 - which probably could have helped our position in the championship for myself and also the team. It's painful, especially because today we were seventh on merit and we had fought for that.
"There are only three races remaining and we really want to do well, because the boys in the garage work really hard day and night to prepare the cars properly. Even this morning they had to change Stoffel's engine and both crews were working together on that, then they prepared for the race and performed some perfect pitstops. Today really was a missed opportunity."
Stoffel Vandoorne: "Today was actually a pretty exciting race for me! Even though it wasn't for any points, I think I put in a very good performance after a difficult qualifying starting from the back. We made a lot of overtakes on merit in the corners, which maybe weren't really expected considering the lack of straight line speed we have. We had a good strategy and some good fights on track, so I'm happy with my pace and I think we maximised our potential today. It was a shame to get so close to the points, but we were always going to struggle starting so far back today with the penalty.
"It's always satisfying when you can overtake on track and we were reasonably competitive, which is encouraging, but we'll have to wait and see for the next few races. We know that some tracks suit us a bit better than others and this one should have been one where we scored points.
"We can't guarantee that we won't have to take more penalties in Mexico, but we'll wait and see and hopefully can make the most of every chance we get."
Eric Boullier: "Today was another race where we witnessed the talent of both our drivers but came home bitterly disappointed and with little to show for it.
"Fernando started brilliantly and was maintaining pace with the pack around him through the first stint and initial round of pit stops. He had the capability to secure seventh or even sixth place and score valuable points for the team, but was denied due to an MGU-H issue which has compounded the problems we've faced all weekend, albeit on the other car. It would seem that despite huge potential, luck hasn't been on Fernando's side in the USA this year, which has been heart-breaking for all of us.
"Stoffel was the unfortunate recipient of 25 further grid drops to add to his existing five-place penalty, owing to an MGU-H problem found this morning which required a full PU change in order to get him out on track in time for the race. This dropped him to the back of the grid at the start, rendering any hopes of points almost impossible. Still, Stoffel drove impressively well here - his first time racing at COTA - with no less than four bold overtaking manoeuvres that went unseen on our TV screens.
"It's a huge shame that these issues robbed us of a strong result at one of the few tracks left this season where we were hopeful of a more positive outcome. The problem encountered on Fernando's car means that Mexico will be another tough race for us, but we'll keep on fighting."
Yusuke Hasegawa: "Today was an incredibly frustrating day for everybody in the team. We came to the United States Grand Prix with high hopes of being able to score some much-needed points, and unfortunately reliability issues across both cars cost us a top-ten finish.
"This morning we detected an issue with Stoffel's MGU-H and made the decision to switch his power unit. This meant he started the race from the back of grid, giving him a tough task for the afternoon. Despite this, Stoffel drove an excellent race today. He overtook cars on track and maintained a good pace throughout. It was unfortunate he couldn't quite score a point to reward his efforts.
"Fernando started today from eighth on the grid and was up into seventh at the start. He maintained his position and kept his rivals behind him, until his race came to a premature end because of an MGU-H issue.
"It's very disappointing that we faced more issues with our PU - particularly because the reliability has been relatively stable in recent races. We will immediately investigate the issue with the Sakura team and work towards a countermeasure for Mexico next weekend."
Check out our Sunday gallery from Austin, here.