England left the field on Saturday evening on a 103 for eight, with a feeble 10-run-lead, after West Indies medium pace bowler Kyle Mayers claimed five wickets for just nine wins. Chris Woakes (9), Jack Leach (1) and last man Saqib Mahmood will need to dig deep to stop an inevitable defeat on Sunday.
Earlier England had allowed West Indies wicketkeeper Josh Da Silva to put together a maiden Test century, during a 52-run last wicket stand with number 11 Jayden Seales, to give the home side a lead of 93.
However, Trescothick tried to put a positive slant on the tour rather than focus on a terrible day on the field.
"It's all gone wrong, yes. We've had a really bad day and we're really disappointed. But it's easy over the course of what we've had over the winter to throw the baby out with the bathwater," he said.
"We believe as coaching staff and players in that dressing room that we've made strides as a team over the course of the Test matches we've had here.
"We've had one bad day today and over the course of the series this is the first bad day we've had. Day one in Antigua we had a challenging day but fought back really well and then in Barbados we were really strong and controlled most of the game.
"Today it's gone wrong, but it's one bad day among 13 other days. We've been better than that over the course of the series but we've not turned up and made it work as we have done in previous games.
"We didn't stand up on the pressure moments when it was going down to the wire."
England made significant changes after the 4-0 Ashes defeat in January, with head coach Chris Silverwood, assistant Graham Thorpe and director of cricket Ashley Giles all losing their jobs while eight squad members were dropped. Among those were record wicket-takers James Anderson and Stuart Broad, both of whom remain highly interested in resuming their storied careers.
Any further hunger for change would centre on captain Joe Root, who has insisted he wants to remain for the long term but is struggling to post the kind of results he needs to back his position.
"I don't think you can pinpoint the captain and say it's his fault. I think it's the group," said Trescothick.
"Everyone will regret what happened because we haven't been good enough as a team and we haven't performed to the level we've put our standards at in the previous two Tests."