DeGale ended up with a cut around his eye, but did enough according to judges, who had him down as 115-113 victor, while the other judge scored it a 114-114 draw.
"It's about time, I'm back on top. Hopefully some doors will open," said DeGale.
"I showed some grit and had to dig deep. His [Wilczewski's] record speaks for himself. He's a good seasoned pro."
"I've got a world ranking now - I'm ranked number two in WBO. I've won the British and European titles in 12 fights and the Olympic gold. I want to fight for the world title by the time of the next Olympics."
DeGale wants another shot at British and Commonwealth champion George Groves, who beat his fellow Londoner in May.