SAN FRANCISCO — A day after getting in touch with his roots, Randy Johnson reached back to give the Giants a start from his dominant past.

Johnson, who surprised the Livermore (Calif.) High baseball team with a private audience on Thursday, took the mound at AT&T Park under drizzly conditions and mowed down the Colorado Rockies in a 3-2 victory Friday night.

With heavier rain forecast to be on its way, Johnson worked quickly while striking out nine in seven shutout innings to secure the 297th win of his storied career. The Giants' bullpen barely protected Johnson's decision, as Brian Wilson worked out of a bases-loaded jam in the eighth to rescue his faltering setup men and record a four-out save.

A day earlier, Johnson reconnected with a time before his five Cy Young awards, his 4,819 strikeouts and his World Series MVP trophy. In the morning, the 6-foot-10 left-hander wandered the Livermore High campus unannounced but not long unrecognized. He visited the police station where his father, Bud, once had a locker. And he spoke to players who button up the same green Cowboys jersey that he did 27 years ago.

"The thing I thought was cool is he showed up by himself," said David Perotti, who has been head baseball coach at Livermore since 2001. "He was walking around the campus and created a huge buzz. He's the most prominent alumnus here, and, you know, he also kind of stands out in a crowd. Nobody had any clue he was going to stop by."

Perotti received a call at 1 p.m. from Sgt. Steve Gallagher, who once caught Johnson in their youth and has a son on the team. Would it be OK if the Big Unit came to practice?

"Randy rolled in at 3 p.m. on the dot," Perotti said. "It was unbelievable. He stayed for two hours. He signed a billion things. He took any picture anybody wanted. He talked to our varsity for an hour and our JV guys for 45 minutes. It was pretty unbelievable. It just seemed to me like he wanted to come back."

Perotti waited until the last moment to tell his players. He didn't want them to send a flood of calls and text messages. When Johnson arrived, it was just the coaches and players.

"He gave the kids the whole 'Work hard' speech, but he wanted them to ask questions," Perotti said. "And nobody could ask anything. Once we got it rolling, it was a lot of fun.

"I can tell you, it's impossible to get a high school kid to be quiet for 20 seconds. And he had them dead silent for over an hour."

Johnson showed Ryan Helms, a senior pitcher, how he adjusted the grip on his slider over the years. Johnson said he plans to visit again, and that he wished he could have done it earlier.

There was just one problem.

"I think I've gotta buy more game balls," Perotti said. "The kids grabbed 'em all for him to sign."

Johnson penned another tremendous start against the Rockies, whom he has defeated 19 times, more than any other team. He struck out the first five batters he faced, didn't allow a runner in scoring position until the fifth and had to pitch out of trouble only once. He punched the air with his fist after getting Todd Helton to ground into a double play with runners at the corners in the sixth inning.

Travis Ishikawa hit a run-scoring double high off the center-field wall in the second inning, and the Giants pecked at Rockies right-hander Ubaldo Jimenez for two more runs.

But the bullpen struggled in the eighth. Bob Howry served up a home run to Chris Iannetta. Jeremy Affeldt allowed a double to Ian Stewart and a pair of infield hits to the left side.

Wilson gave up another infield hit, to Garrett Atkins, that shortstop Edgar Renteria smothered to keep the tying run from scoring. With the bases loaded, Wilson struck out Ryan Spilborghs on a 3-2 fastball to preserve the lead.

Wilson, who is growing out a mullet as a tribute to Johnson, issued a one-out walk in the ninth before striking out Stewart to end it.