Fletcher scored a belter for his country against Poland, before backing up that display by netting a hat-trick against Gilbraltar.
The 30-year-old also netted in Sunderland's last game before the international break against West Ham United, meaning he is full of confidence at the moment.
And Allardyce said: “One massive positive is Steven Fletcher scoring goals.
“I saw the goal he scored against West Ham and then he’s scored at international level.
“The two most important guys on the football pitch are the goalkeeper and the goalscorer. That starts you to build a spine.
“We’ve got goalscorers and if they carry on, we just have to stop them going in at the other end – and that’s an easier task than scoring goals, I’ll tell you.”
Fletcher's run of form has been his most productive in a long time, as the former Wolverhampton Wanderers forward has struggled for goals at times.
Fletcher notched just five goals last season, and he hit the back of the net only once in his first nine appearances this time around.
However, he will be hoping that he can stretch his current run, and prove to be a valuable asset under Allardyce's leadership.
Sunderland's next match comes against West Bromwich Albion on Saturday, with the North East outfit still looking for their first Premier League win of the season.