After three league defeats, Ross delivered a dominant display to overcome their visitors from Paisley.
Ross took the lead in the eighth minute when Kettlewell fired into the top of the net from the edge of the 18-yard box, and Brittain grabbed his first in the 24th minute after David Cornell stopped his penalty but could not prevent him pouncing on the rebound.
Brittain ended St Mirren's hopes with the third goal after 57 minutes.
Adams said: "It was a very good performance. We thoroughly deserved the victory, we did well defensively and created a lot of chances today. We pressed them very high up the park.
"It was a terrific goal from Kettlewell to start the game. Then Richard Brittain follows up from the penalty and gets another good finish from the short corner. It was also nice to get a clean sheet and score three goals.
"There are a lot of good players at the football club - they passed the ball well and created chances. It [the victory margin] could have been more than it was. But I'm just happy to get a clean sheet."
Adams added: "We didn't play well in the last two games against Partick Thistle and St Johnstone.
"But today we deserved the three points. St Mirren have a lot of experience throughout their team and we knew it was going to be a tough game for us today. But we closed the experienced players in their side down and created a lot of openings in the match."
His opposite number, Danny Lennon, was perturbed by some of St Mirren's play.
Lennon said: "We knew it would be challenging coming up here. Apart from Celtic, Ross County had the best home record last season. But I thought we were ready for that challenge - we started all right, there was a lot of pleasing stuff throughout.
"The over-riding emotion just now is we are all very frustrated.
"We have a lot of quality and character in that dressing room, a lot of players who can turn a game - potential match-winners.
"But we also have players out there that are costing us with lack of concentration.
"We have to make sure we overcome that. We have certainly created enough opportunities over the last couple of games in the final third but we are just not getting over the line."
Lennon is confident his side will overcome their slow start to the season.
He added: "The goals we are conceding are very disappointing and frustrating. But I believe in the group of players we have and we will come through this difficult time together."
- Sports & Recreation
- Stuart Kettlewell
- Richard Brittain
- St Mirren