Van Persie scored his 15th goal of the campaign as United recorded a 3-1 win over Sunderland at Old Trafford to remain six points clear of Manchester City at the top of the Barclays Premier League.
"Robin van Persie was a great purchase," said O'Neill. "It means Manchester United are capable of scoring goals because Wayne Rooney is a top quality player as well.
"Whilst their main players stay fit Manchester United are capable of winning the league."
O'Neill certainly wished some of the criticisms that have been levelled against United could be said of his own team now that United will definitely be top on Christmas Day.
Tom Cleverley's first Premier League goal at Old Trafford was followed by Wayne Rooney's fifth in four games to put the hosts in control, before Frazier Campbell grabbed a consolation against his former club.
"People keep saying we are weak in midfield but these guys are very good players," said Sir Alex Ferguson.
"Sometimes it gives me a little problem selecting the right two, although today was simple because (Michael) Carrick and Cleverley deserved to play after their performance (against Manchester City) last week."
Cleverley is making an impact in the Paul Scholes role, with Ferguson admitting he should be scoring more often after taking his overall United tally to three.
"Tom has goals in him," said Ferguson. "As a younger player he always had a goal in him. He has got me three this season and I really do expect more from him because he is a nice finisher."
Source: PA
Source: PA