Head coach Matt Maynard and his side were left to rue a second innings batting collapse which enabled Middlesex to secure a 10-wicket victory at Lord's.
The Welsh county looked in a comfortable position when David Lloyd and Eddie Byrom put on a 123-run partnership opening partnership, before all ten wickets fell for 97 runs, which meant the home side required just 45 for victory.
Middlesex now move into the second promotion spot in division two with a 12-point lead over the Welsh county with two rounds to play.
“We had a poor session with the bat and it’s cost us the game, essentially," said Maynard.
“After watching Dave (Lloyd) and Eddie (Byrom) play as they did, putting on that 123 and going at four an over and making it look very easy, maybe a bit of complacency set in.
“We lost some poor wickets. There was no momentum and we didn’t try and wrestle any back, so we’re bitterly disappointed.
“We’re looking for one of our guys to get a big hundred to put us in a position to score 400 runs and we haven’t managed that in the last two Championship matches.
“So we need to get that right for the last two games if we’ve got any chance of promotion. We need to get maximum points from both games to stand any chance.”