The Sunderland manager says he is delighted with his new striker's goal-laden beginning to his Mackems career and that he always knew the Scotland international would be a success
The 25-year-old notched his fifth goal against Wigan in only his fourth league start for the Black Cats since his £12 million move from Wolves to give Sunderland their first Premier League win of the season.
There were some that questioned Fletcher's price tag and his ability to score regularly in the Premier League, but O'Neill says there were never any doubts at Sunderland that the Scotland international would find the net.
"We're very pleased with how quickly he's settled," O'Neill told reporters. "I could see his qualities when he played at Wolves and he's done everything I could possibly ask for.
"Of course you're delighted when someone you sign makes such an impact, but I have to say it hasn't really surprised me."
While Fletcher's goals may have got the plaudits, O'Neill went on to stress that there was more to the striker's game than simply his finishing ability.
O'Neill added: "He's got his goals, yes, but it's his all-round play and I think the crowd have taken to him. He's been brilliant for us."
The victory over Wigan crowned a positive week for O'Neill's team, who also progressed to the next round of the League Cup after seeing off League One side MK Dons. The Black Cats are set to face a real test next however, as they travel to the Etihad to take on champions Manchester City.