He threw a two-hit shutout with 14 strikeouts in his postseason debut in 2010. He then won Game 1 of the World Series, against the Texas Rangers, and threw a gem in Game 5, the one that clinched San Francisco’s first title. His line score was eight innings, one run, 10 strikeouts.

Back then, his father would call him after almost every start, and they would talk about what he saw and how Lincecum felt. They would always discuss his mechanics.

One day, the feeling was gone, he said. His delivery was in disarray.

His velocity started to drop. (His fastball averaged 89.6 miles per hour this year, about 4.6 m.p.h. slower than in his rookie year, according to FanGraphs.com.) His slider and curveball started to lose their bite, too. He had losing records in three of the last four seasons. And over the last three years, his combined E.R.A. was 4.76.

Meanwhile, Lincecum stopped talking to his father as much about his delivery.

“I guess that’s me maturing in my own way,” Lincecum said.

During the 2012 postseason, as the Giants twice rallied to win another World Series title, Giants Manager Bruce Bochy first moved Lincecum to the bullpen, where he thrived. In 13 innings in relief, he struck out 17 batters and only allowed one run. The one game he started — in the N.L.C.S. against the Cardinals — did not go as well. He allowed four runs in a loss.

Not surprisingly, Bochy tried a similar tactic again this season: Near the end of August, he again moved Lincecum to the bullpen, in part to give him time to tinker with his delivery. But in this instance, the move did not work. In two of his six appearances, Lincecum allowed a combined seven earned runs. So it seems almost understandable that he has yet to pitch in this year’s postseason, although it is not as if he is in the manager’s doghouse.

“He’s done a lot for us,” Bochy said recently. “I haven’t forgotten that.”

Lincecum has appeared to take all this in stride. His teammates say that he still sings in the clubhouse and tells jokes and stories in the bullpen. In interviews, Lincecum maintains that he is willing to do anything for the team.