If Nelson can hang on to win the San Antonio tourney, he would become the oldest winner in Champions Tour history.
His 4-under-par 67 Saturday allowed him to finish 36 holes at 10-under 132 -- one shot better than Jay Don Blake (64), Steve Lowery (67) and Chien Soon Lu (68), who where knotted in second place at 9-under 133.
Nelson won San Antonio in 2001 and has 19 career victories on the senior tour, but none since 2004.
The oldest winner in tour history is Mike Fetchick, who took the 1985 Hilton Head Seniors International on his 63rd birthday. Nelson will be 63 years, one month and 21 days old Sunday.