- Premier League
O'Neill: Van Persie is United's Messi
O'Neill's side suffered a 3-1 defeat at Old Trafford on Saturday, in which Van Persie opened the scoring to take his tally for the season to 15 from just 21 appearances in all competitions.
The Dutchman has been the match-winner for United on several occasions already this term, most recently in the 3-2 derby win at Manchester City the week before the Sunderland match.
And O'Neill believes that United now have a player who compares to reigning World Player of the Year Messi in terms of his importance to the team.
"With players of the calibre of Van Persie in your side, you always have a chance of winning football matches," O'Neill said.
"Would, for instance, Barcelona have the same effect if Lionel Messi didn't play? The number of goals Messi has scored is incredible. They are a very talented team but without him, you don't know, because Messi is their talisman.
"Honestly, Van Persie can get goals out of very little. It looks like nothing is happening and you have players there in the area. But all of a sudden he has opened up a gap."
United beat Premier League champions Manchester City to Van Persie's signature in the summer, and O'Neill said that has seen them steal a march on their local rivals in this season's title race.
"You always felt that United would give themselves a big edge by getting Van Persie," he said. "He was a great purchase. It means Manchester United are capable of scoring goals because Wayne Rooney is a top quality player as well.
"We are making judgments before Christmas here - but if Van Persie stays fit, that will make a massive difference to United's challenge. They have a great chance of winning the league.
"United have paid close on £30 million for a player who had just one year left on his contract, so that might tell you how valuable they perceive him to be.
"But it's not just the perception, the reality is that he has been fantastic so far."