Estes, who turns 33 on Feb. 18, is 13-5 in 23 career appearances against the Padres and 99-89 with a 4.71 career ERA in 273 games, including one relief appearance.
The 6-foot-2, 219-pound native of San Bernardino, Calif., was 7-8 with a 4.80 ERA in 21 starts for the Diamondbacks in '05. He split two decisions against the Padres with a 2.57 ERA in two starts.
Estes' best season was 1997 when he was 19-5 with a 3.18 ERA in 32 starts for the Giants, making the National League All-Star team. He has visited the disabled list seven times with shoulder problems but has been free of shoulder woes since 2001.
"He's a fly-ball pitcher who should be effective in our ballpark, especially with our improved outfield defense," Towers said. "He can handle the bat, too."
He didn't show it in '05, hitting .069 in Arizona, but he batted .236 in Colorado in '04 and is a .158 career hitter with four homers. The right-handed hitter batted .206 with a homer and 10 RBIs for the Giants in 2000.
Estes is 1-0 with a 3.15 ERA in three career starts at PETCO Park, with the Rockies in 2004. Estes was 15-8 that season before choosing the Diamondbacks in free agency, with the Padres also in pursuit.
He turned down a scholarship from Stanford to sign with the Mariners as their first-round choice (11th overall) in 1991 out of Douglas High School in Minden, Nev.
Estes likely would join Jake Peavy, newcomer Chris Young, Woody Williams and Chan Ho Park or Clay Hensley in the rotation, with Tim Stauffer, Dewon Brazelton and Rule 5 acquisition Seth Etherton also expected to make bids during Spring Training.
The Padres on Tuesday agreed to terms with Brazelton on a one-year contract and with catcher Todd Greene on a Minor League contract with an invitation to Spring Training.
Brazelton, 25, went 1-8 with a 7.61 ERA in 71 innings for the Devil Rays in 2005. At 24, the right-hander was the Major Leagues' second-youngest Opening Day starter last season.
Originally the third overall pick in the 2001 First-Year Player Draft, Brazelton was acquired from Tampa Bay in exchange for third baseman Sean Burroughs on Dec. 7. He was not offered arbitration, signing a free-agent deal. Brazelton has a career record of 8-23 with a 5.98 ERA in 54 games, including 41 starts.
Greene, 34, batted .254 with seven home runs and 23 RBI in 126 at-bats for the Rockies in 2005. He was limited to 38 games after suffering a strained right hamstring on June 5.
Over parts of 10 Major League seasons with the Angels, Blue Jays, Yankees, Rangers and Rockies, Greene has a career batting average of .248 with 69 home runs and 200 RBIs in 475 games.