Thistle took a deserved lead into the break after Kris Doolan scored following an 18th-minute corner and last season's fifth-placed side could not sort things out at half-time.
Steven Lawless netted twice for the Scottish Premiership newcomers early in the second period after linking up well with Stuart Bannigan.
And Graham Carey's deflected goal proved scant consolation for Adams.
"We didn't do well enough," Adams told BBC Radio Scotland.
"I think it's probably the worst performance I've had since I became Ross County manager.
"The players who came in didn't do well enough and the players we had last year didn't perform.
"I didn't see us forcing a way back into the match. We should have pushed forward a bit more, but it was a bit of anxiousness in our play after we lost a couple of goals.
"When we got into good areas, we didn't pick out the right option, but defensively, we didn't look solid - there were gaps all over the pitch and from that point of view, we need to get back to what we were doing well.
"We didn't pass the ball well enough, we didn't get close enough to the Partick Thistle players - we have to do that better.
"Individually, the players have to look at themselves and perform better next week."
Adams had warned before the game that their successors as First Division champions would play with a confidence and momentum carried on from last season.
"I thought Thistle played well, they closed us down, passed the ball well and they were energetic," Adams said.
"They played with a freedom that you get when you win the First Division.
"But it's only two games in to a season, and from my point of view, it's too early to predict anything."
Thistle boss Alan Archibald was delighted to see his team carry their work from during the week into Saturday's contest as they built on their opening draw with Dundee United.
"We showed our confidence and I think a couple of the guys up the pitch like Steven Lawless and Stuart Bannigan were unplayable," he said.
"All of it comes from a good back line and good organisation in the field.
"We work hard in training and every game deserves its merits to work hard. You have to change things for some teams you play against, and I think it worked."