Denver ? A leadoff walk, a couple of boos. A single, and a few more fans join in. Then the tying run crosses the plate. By the time it’s over, it seems every fan is letting Colorado closer Shawn Chacon have it after blowing another save chance.

“Throwing in the thin air and with everything Coors Field has to offer, I would definitely say it’s the toughest job in baseball besides late-inning pinch-hit guys,” San Francisco Giants closer Matt Herges said. “It’s got to be in the same ballpark.”

The right-hander was an All-Star as a starter last year, but he was easily the best option for a team that didn’t have the money to get a big-name closer and not much to choose from within the organization.

It hasn’t been as smooth as Chacon or the sagging Rockies would have liked.

Struggling with his command — 31 walks in 41 1/3 innings — and the urgency that comes with pitching in tight games, Chacon has been either very good or very bad.

Chacon has blown seven of 28 chances and is line to become the first pitcher in major league history to save 20 games and have an ERA over 7.00. He had a 7.40 ERA heading into the weekend.

Chacon has allowed at least two runs in nine of his 42 appearances — all an inning or less — and has given up 49 hits, including nine homers.

“We didn’t expect it to be the roller coaster ride that it’s been,” Rockies manager Clint Hurdle said.

When he’s hitting his spots with his fastball, Chacon is as good as they come, with the kind of stuff Herges calls “absolutely electric.” Chacon proved that when he ended the first half with nine straight saves, finishing with 20 by the All-Star break.

As a starter, Chacon would have and inning or two to figure out where the ball was going and make adjustments. He doesn’t have that luxury with the game on the line and it’s led to plenty of anguish for Chacon, the Rockies and their fans.

“I’ve hit rock bottom this season,” Chacon said. “The thing now is bouncing back. It took me a while to figure out how to bounce back and what I need to do. Anytime you go out and blow some saves, it makes you tougher mentally. That’s the life of a closer.”

Colorado's Shawn Chacon reacts as he struggles to close out the Boston Red Sox in this June 16, 2004 photo. Chacon has had a rocky season trying to adjust to his new roll as the team's closer.