The 20-year-old was a surprise inclusion in Arsene Wenger's starting XI at Old Trafford, with Manuel Almunia ruled out of the top of the table clash and doubts over the fitness of Lukasz Fabianski.
Szczesny enjoyed a promising Premier League debut, producing a string of second half saves to keep the hosts at bay.
But the young Polish 'keeper thought his preparation for Rooney's wayward spot-kick was more rewarding than the stops he made.
"I did prepare myself for a Rooney penalty before the game. I actually decided to try to delay him, show him my presence and hope for the best," he said in the Mirror.
"Maybe my presence put him off and made him miss it.
"It's obviously a mental battle between the goalkeeper and the striker, a psychological battle, so I tried him and stand off my line for as long as possible, until the referee put me on the line. Then I made myself big and he missed."
"People were congratulating me for the saves in the second half but I don't think they were fantastic stops," he continued.
"Anderson pretty much hit it straight at my chest because I was in the right position at the right time and the second one, I don't think Rooney connected very well.
"I was a little bit scared when he took it on but if it had been a little bit higher, as he was trying to do, I maybe wouldn't have got it."
