Martinez was knocked down in the seventh round but recovered to inflict a cut above Pavlik's right eye that turned the bout back in his favor in the ninth. The Argentine built on that momentum and earned a unanimous points victory.
"It was a 12 round plan," Martinez said. "I knew in the long run he would show his true championship colors. But I knew at the end I had to finish off strongly."
Martinez (45-2-2) dominated the early stages with superior speed and footwork, darting in and out and landing right jabs and straight lefts.
His movement left Pavlik (36-2) off balance, causing him to lunge with his punches and allowing Martinez to land counters over the top of the American's jab.
Pavlik, however, began to close the distance in the fifth round and cut off the ring more effectively.
Martinez walked into a short right hand that dropped him to the canvas in the seventh round and while he appeared unhurt, the knockdown added to the sense the contest was slipping away from him.
But the Argentine turned the tide two rounds later, opening up a cut above Pavlik's eye.
"At the beginning of the ninth, he landed a good shot and he cut me," Pavlik said.
"I couldn't see. It was like a whiteout in my right eye. I could still see punches, but he fought a smart fight, doubling on the left hand. He'd throw a left, I'd block it, and he'd throw another one.
"He wasn't hurting me or nothing, but he was catching me with punches, and it looked bad.
"There's nothing you can do about that."
(Writing by Kieran Mulvaney in Washington D.C.; Editing by Peter Rutherford and Greg Stutchbury; To query or comment on this story email email@example.com)