The Scots edged out their visitors at Hampden Park, Glasgow to move up to second position in Group F thanks to an own goal from Martin Skrtel in the 89th minute.
However, Gordon Strachan’s charges still need to beat Slovenia away on Sunday to ensure they finish second in the group and keep their play-off chances alive.
“We’ve only done half the job,” said Fletcher, as quoted by the BBC.
“We’re going into the game in Slovenia in great confidence and it’s all down to that last game and a position that we’d have taken a long time ago, but we’ve still got to go out there and get the performance and the result that sees us over the line.
“You have many massive games in your career and this is another one.
“That momentum’s definitely in our favour just now. We’ve just got to see it over for one last game but then we’ve got a play-off after that so there’s still a long way to go.
“It’s not an easy game to go to Slovenia but it’s in our hands, that’s all you can ask for. We know what we’ve got to do.
“We believe in ourselves. We’re full of confidence. No matter what players play, we’ve got a good squad. All these things are coming together. We’re patient.”