Birtles believes the £8m Mexican has had the goalscoring good fortune that he and his 2002 counterpart Diego Forlan didn't have when they joined United.
"Chicharito scored a fortunate goal in the Community Shield against Chelsea when the ball screwed off his foot and went in off his face," he told the Manchester Evening News.
"That's the kind of luck any new striker wants.
"You sometimes need those that go in off your backside to get you off the mark or keep a run going.
"On my debut against Stoke City I had a good chance and rounded their keeper but it had been raining heavily that night at the Victoria Ground and their full back Ray Evans aquaplaned in and cleared my attempt off the line.
"The next match was my Old Trafford debut and I hit the post after rounding the keeper again.
"If those had gone in we would be talking about a dream start for me."
"Diego suffered the same way. But it is good for Hernandez that he was off the mark early."