Posey noted that Lincecum threw more than 200 pitches all night, including 40 in the bullpen warming up pregame and then eight pitches before each inning.
"It takes a toll on your body, so for him to be able to continue to execute pitches is remarkable," the catcher said.
Manager Bruce Bochy said he had pitching coach Dave Righetti — who threw a no-hitter for the New York Yankees on July 4, 1983 — check on Lincecum the last few innings.
"I'm superstitious at that point," Bochy said. "I'm not going to say anything. There was no way he was coming out. I was just praying he didn't hit the 150 mark.
"He was just right on all night with all his pitches," Bochy said.
Lincecum was in a season-long funk. He was the loser when Cincinnati's Homer Bailey no-hit the Giants on July 2.
Pablo Sandoval did his part, too, when he made a nice backhanded play on pinch-hitter Jesus Guzman's grounder deep behind third base and threw him out for the third out of the seventh.
Lincecum had been struggling coming in, losing his previous four decisions and hadn't won since June 4 against Toronto. He hadn't won on the road since April 3 at the Los Angeles Dodgers. Then again, he'd gotten only 12 runs of support in his last 10 starts.
The crowd gave Lincecum a standing ovation as he headed to the mound for the ninth.
Lincecum struck out Chase Headley and then retired Carlos Quentin and Alonso on fly balls to left.
Lincecum tossed the 15th no-hitter in franchise history and seventh since the Giants moved to San Francisco after the 1957 season. Matt Cain was perfect last June.
The Padres remain the only team without a no-hitter.
Lincecum lost 15 games last year and ended the season as a reliever — and a reliable one at that. He cut his hair short in the offseason, a new look as he started anew. He worked out with a personal trainer during the winter to add about 10 pounds of strength, and tweaked his mechanics.
Padres manager Bud Black said Lincecum was mixing his fastball, splitter, curve and cutter.
"He's evolved," Black said. "He knows how to pitch. He keeps his poise. He has us off-balance all night."
The Padres lost for the 18th time in 21 games and dropped a season-high 13 games under .500.
"We haven't been swinging the bats like we're capable," Black said. "We're not pitching. There's a lot of things we're not doing well. The last 2 ½ weeks have been unacceptable. We just haven't gotten it done."
While Lincecum dominated the Padres, the Giants jumped all over San Diego's Edinson Volquez (6-8).