Danny Lennon admitted his side need points to avoid a play-off place after .
John McGinn struck a second-half equaliser to cancel out Yoann Arquin's opener, but Melvin De Leeuw hit a deserved late winner for the hosts.
"It's a difficult one to take," Lennon told BBC Radio Scotland.
"We came out of the traps very well in the first 15 minutes but then we lost our way. That's the 30 minutes where we've lost it in the first half."
Despite the tight score-line, Ross County were well worth their win in Dingwall, leapfrogging the Buddies in the Scottish Premiership table.
With Partick Thistle picking up three points against Aberdeen, it leaves Lennon's men languishing in second bottom.
Lennon said: "It's still very nip and tuck, it's going to be the ones that put the most consistent run together that are rewarded. It's very important with 12 games remaining.
"I feel that we've certainly strengthened the group in January, that takes a little bit of time to click. It's the first time we've had all the new players available for selection."
Lennon refused to comment about the incident that led to himself and Ross County boss Derek Adams being sent to the stand.
The two exchanged words on the touchline following a clash of heads between Jim Goodwin and De Leeuw, with the Victoria Park boss feeling the St Mirren captain was at fault.
"I was absolutely delighted with the response the players gave me and carried out everything that was asked of them," added Lennon.
"We then get ourselves back into the game and were really taking the ascendency to Ross County. We get caught on the hop and the second goal's a race at the end.
"We can't just compete for 60 minutes. We've got to make sure we're playing for the full 90."