The pair were also given five-second timed penalties, which saw both demoted by one position.
Both men took their tally to three penalty points but it is irrelevant with neither men on the grid for the 2019 season.
Vandoorne secured P14 on track before the penalty, and was proud of his performance in Interlagos.
“Maybe no one noticed again, but it was a great race again today,” Vandoorne said.
“We did a good job in the first stint, made the tyres last a little bit longer than the others, came out on the fresh tyres, had a good fight with Fernando and from there on we did a good race.
“We managed to overtake the Williams as well.
“It might not look on the timing board like it’s been a great race, but I feel like today I maximised everything so I’m happy.”
Alonso’s strategy did not work on Sunday afternoon, with an early-stop backfiring as he ran most of the race as the last of the runners.
He was able to get past both Williams before the end of the race, but admitted that it was a tricky one in Brazil.
“It was tough today. We gambled on the strategy a little bit, stopping very early. It didn’t work,” Alonso said.
“With the medium tyres we blistered the tyres and we were not competitive in the second half of the race.
“The pitstop was not clean and smooth so we lost a bit of time in there.
“Overall we’ve been too slow all weekend. We didn’t have the pace to be in the top 10 so whatever strategy, whatever we tried the points were unreachable.”