Cook was playing in just his second tournament on the senior circuit, and he beat his good friend Mark O'Meara by one stroke. O'Meara is still searching for his first senior victory.
"It was not easy out there. Some tricky winds on a good golf course and major championship winners all over the place. Thrilled? I guess I would be thrilled."
Cook won 11 times on the PGA Tour, including once in Texas at the 1998 Byron Nelson Classic. His first win came in 1981, and his most recent before Sunday was at the 2001 Reno-Tahoe Open.
AT&T Championship story
AT&T Championship scores