Once lights-out, the Giants’ Tim Lincecum becomes a liability

It has been eight years since that Steve Finley grand slam, eight long years since the last truly great race between the Dodgers and the San Francisco Giants.

The Dodgers and Giants have distanced themselves from the pack in the National League West this year, and the rivals face off in the final series of the regular season. Imagine the intensity if the division championship were to come down to that one last game, Clayton Kershaw for the Dodgers and Tim Lincecum for the Giants.

Make that “anybody but Tim Lincecum” for the Giants.

In a season in which so much has gone so right for the Giants, their two-time Cy Young winner is enduring a disaster of historic proportions. By one measure, no one has pitched a full season with a performance so poor in 97 years.

The traditional benchmarks speak loudly enough.

The Giants are 2-10 when Lincecum starts, 31-15 when one of their other four starters does.

His earned-run average of 5.83 is the second-worst in the league. On Sunday, Lincecum draws the Texas Rangers, the highest-scoring team in the major leagues.

That is discouraging for any team, urgent for one that depends on its starting pitchers to convert three or four runs into victory.

“We talk about pitching being our strength,” Giants Manager Bruce Bochy said. “That’s the key to us having a successful season — five starters giving you a chance to win.”

Ryan Vogelsong and Matt Cain rank among the top five in the league in ERA, with Vogelsong at 2.26 and Cain at 2.41. Madison Bumgarner (3.24) and Barry Zito (3.26) rank among the top 25.

The Giants’ bullpen ranks third in the league in ERA, despite the season-ending injury to closer Brian Wilson. In his absence, Santiago Casilla has converted 14 of 15 save opportunities.

General Manager Brian Sabean bet Vogelsong had not been a one-season wonder at 33 and traded talented but erratic pitcher Jonathan Sanchez to the Kansas City Royals for outfielder Melky Cabrera, who leads the majors with a .364 batting average. Sabean also won big in swapping center fielders with the New York Mets, flipping Andres Torres for Angel Pagan.

The Giants could use some offense from third baseman Pablo Sandoval, activated Saturday from the disabled list even as he faces a sexual assault investigation, from second baseman Freddy Sanchez, on the disabled list all season because of shoulder and back injuries, and from anybody at first base.

“The offense is always going to be a work in progress,” Sabean said. “We needed a rebound year from [Aubrey] Huff. That didn’t happen.

“We’re scoring enough runs to keep things interesting.”

Nothing has been quite so interesting about the Giants this season as the decline of Lincecum. He finished last season third in the league in strikeouts, fifth in ERA, sixth in Cy Young voting.

Then came this season.

Statistical analysts rank pitchers by adjusted ERA, or ERA+. The figure takes into account how pitchers perform against their peers and how ballparks influence performance — that is, a 3.00 ERA is more impressive in the steroid era than the dead-ball era, and more impressive in Coors Field than AT&T Park.

An ERA+ of 100 is average, and higher is better. In 2008, when Lincecum won his first Cy Young award, he led the league with an ERA+ of 168.

Lincecum had an ERA+ of 60 as of Friday. The only pitchers in major league history with a lower ERA+ over a full season: Rube Bressler of the 1915 Philadelphia Athletics, and Gene Wright, who split the 1903 season between the Cleveland Naps and St. Louis Browns.

The obvious culprit is a loss of velocity. According to fangraphs.com, Lincecum’s average fastball velocity has dropped from 94 mph in 2008 to 92 mph last season and 90 mph this season.

“I know what has been said about his velocity, but it’s real close to what he pitched with in the postseason 2010,” Bochy said. “That is a non-issue for us.

“With that said, these guys all want to throw 96 or 97. After so many innings, they all lose a little velocity. They all have to make an adjustment.”

It is not so much the decreased velocity itself as its effects — a lesser difference between a fastball and an off-speed pitch, a smaller chance to get away with a fat pitch. Batters are drawing more walks off Lincecum, hitting more line drives, hitting fewer ground balls.

“The mistakes aren’t getting popped up,” Sabean said. “The league has made adjustments. He needs to make adjustments back.”

In five of his starts, Lincecum has given up four or five runs in one inning, but no more than one run in the remainder of the outing.

“He can’t do damage control in an inning,” Sabean said. “Things go haywire.”

Said Bochy: “He’s healthy. He’s throwing the ball well at times. You can see how close he is. He just has an inning where he gets out of rhythm.”

Jake Arrieta has a 6.32 ERA; the Baltimore Orioles removed him from their starting rotation on Saturday. Mike Minor has a 6.57 ERA; the Atlanta Braves just skipped one of his starts.

Lincecum has earned a more comfortable spot in the San Francisco rotation. As Zito knows all too well, no pitcher can adjust to decreased velocity overnight. With Lincecum, the Giants say they see progress.

“We’re going to keep throwing him out there,” Bochy said. “We need him.”

Sabean sees brighter days ahead too — and a lack of alternatives. He traded the Giants’ top pitching prospect, Zack Wheeler, to the New York Mets last season, to rent outfielder Carlos Beltran.

In San Francisco, they trust in Lincecum. They have to.

“You still have to have five starters,” Sabean said. “I don’t know where you would turn.”

bill.shaikin@latimes.com

twitter.com/BillShaikin