Sunderland had taken a 52nd-minute lead with a delightful counter-attack neatly finished by Kieran Richardson's first-time strike into the top corner before Wolves staged a remarkable turnaround.
Facing the prospect of going two goals down at home, Wolves keeper Wayne Hennessey dived the right way to save a Sebastian Larsson penalty in the 73rd minute and his team mates took less than 30 seconds to fashion an equaliser off Fletcher's head.
Fletcher was on target again eight minutes later with a half-volley but Sunderland will feel aggrieved after Wolves midfielder Jamie O'Hara appeared to handle the ball.
The win lifted Wolves to 15th with 14 points from as many games, while Sunderland, whose new boss O'Neill was watching from the stands after his appointment on Saturday, were left sitting one place and one point above the relegation zone.
Earlier in the day, Stoke ran out 1-0 winners at Everton thanks to a 15th-minute goal from defender Robert Huth. Stoke Climbed to eighth in the table, two places above Everton.
Manchester City crushed Norwich City 5-1 on Saturday to maintain their five-point lead at the top over champions Manchester United who won 1-0 at Aston Villa.
Tottenham Hotspur beat Bolton Wanderers to stay third, fourth-placed Chelsea won 3-0 at Newcastle United and Arsenal climbed to fifth with a 4-0 victory at Wigan Athletic.
Fulham host Liverpool on Monday.
