With the bases loaded and two outs in the fourth inning, Barton smashed Lincecum's first pitch low and up the middle. The ball hit Lincecum's leg during his follow-through and caromed halfway back toward home plate, where catcher Buster Posey picked it up and threw to first base for the inning-ending out.
Meanwhile, Lincecum skipped toward first base in pain before collapsing onto his hands and knees. Manager Bruce Bochy and head athletic trainer Dave Groeschner raced toward Lincecum to check on the two-time Cy Young Award winner. After a brief consultation, Groeschner and assistant trainer Eric Ortega flanked Lincecum and led him toward the X-ray facilities.
Lincecum said he initially experienced a sensation akin to paralysis but quickly felt fine.
"I'm not too worried," he said. "I knew it hit me in a relatively good spot. It didn't hit me in the front of the kneecap."
Lincecum's status for his initial start of the 2014 regular season, scheduled for Thursday at Arizona, was uncertain. Much could depend on the condition of his knee on Saturday. Whether Lincecum avoids swelling could be a significant factor.
"Things are looking positive, the way I feel right now," Lincecum said in typically upbeat fashion.
Said Bochy, "If I had to guess right now, I'd say he'll be OK to start. But I think we'll have a better idea tomorrow."
Bochy mentioned Yusmeiro Petit, the long reliever who pitched a scoreless fifth inning in Friday's 4-1 loss to Oakland, as a possible replacement if Lincecum is unable to face Arizona. Conceivably, if Lincecum needs only slightly more recovery time, he could exchange assignments with No. 5 starter Ryan Vogelsong, who's slated to face the Dodgers next Friday.
The Giants were relieved that a member of their starting rotation, who happens to be among the most popular players in the clubhouse, averted disaster.
Bochy pointed out that Barton's drive hit Lincecum squarely. "The ball didn't ricochet left or right," Bochy said.
Said Posey, "It's reaction to go after the ball, but at the same time, you're running out there, picking up the ball and thinking, 'He just got whacked hard.'"
In an incident vaguely similar, Lincecum left a start after 4 1/3 innings at Houston on Aug. 12, 2008, when Brad Ausmus smashed a line drive off his right kneecap. Lincecum made his next scheduled start on his regular four days' rest and lasted 7 2/3 innings, yielding three hits and striking out 10 in a 3-1 Giants victory at Atlanta.
Possessing a gymnast's flexibility, the 29-year-old has missed only one start in his 6 1/2-year Major League career due to physical reasons, on Sept. 8, 2009, against San Diego. Back spasms sidelined Lincecum that game, prompting the Giants to summon left-hander Madison Bumgarner from Double-A to make his Major League debut.