Van Persie, who claimed the golden boot in the Premier League last season, struck twice in the 4-1 away win over Swansea, with Danny Welbeck matching his contribution.
And Spaniard Michu was impressed with what he saw.
"He had two chances and he scored two goals, but that is why Manchester United are fighting for the championship," he said.
"For me, to be honest, he is the best striker in the world. He had no clear chances in this game and it is just incredible how he ended up with two goals. It stops with him, he is the best.
"I don't know how many goals he will score this season. A hundred, maybe a thousand! One thing is for sure, he is going to score a lot."
Swansea will now look to bounce back from the loss when they host Petrolul Ploiesti in the first leg of the UEFA Europa League play-offs on Thursday.
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