Mexico was one of the worst F1 events for Haas in its debut season last year and team boss Gunther Steiner said this year's edition presented "one of the worst scenarios" for the outfit.

That turned out to be the case, with Kevin Magnussen 18th and Grosjean 19th, 2.9 seconds off the pace, behind both Saubers which are running the old-spec Ferrari engine.

"We were braced for a tough one but I was hoping that the problem we had last year would get a bit better," said Grosjean.

"In China, we struggled in 2016 and we weren't that bad this year. Without the yellow flag, we could have gone to Q3. Some races where we have improved, some others where we haven't at all and this is one of them.

"We're not super good on tyre usage, but I don't think today that is the biggest problem. We have two set-ups which are different between the cars and we haven't got one that is outstandingly good compared to the other one.

"So I think today is a bit of a slap in the face, a wake up call, and we need to put our head down and try and understand why we are slipping away through the season.

"We know how much horsepower we have compared to Sauber and they are in front of us. It shows we need to do things better.

"I guess everyone has brought performance and we haven't that much. It's the only explanation I've got."

Magnussen added: "The frustrating and confusing thing is we've got a car that at some tracks can be fighting for top-six and then other tracks we're last.

"That's confusing so we need to improve our understanding of where the performance is."

As was the case last year, Haas has fallen down the pecking order as the season has gone on, with better funded outfits like Renault move ahead in terms of performance.

Grosjean said ensuring Haas can stay in the fight until the end of the year in 2018 needs to be the team's main goal.

"I don't want to say it's worrying because I'm confident we can produce a good car for 2018 as we have done the previous two years," he said.

"One pattern is we start good and then we drop back. That is something we need to improve. We need to put our head down, we need to understand and we need to make sure we keep improving the car and that the updates are working.

"Renault has done super well [this year]. They started with good pace in Melbourne, they dropped back a bit, and then it's been up there since.

"They beat one Force India today so they can argue they are almost the fourth fastest team on the grid."

Steiner added: "We are not good enough. I think we know why we are where we are here. Are we happy with the situation? No. But this is what we face, and for next year and these conditions we need to do better work."