DENVER -- The Giants spent the season's first seven weeks reminding the league that, when healthy, they remain a force to be reckoned with. In one explosive inning Tuesday night, the Colorado Rockies sent the same message back to the National League West's early leader.

Nolan Arenado's double off Sergio Romo gave the Rockies a 5-4 walk-off win at Coors Field and moved them within two games of the Giants in the West. With power bats to spare and a pitching staff that's expected to get healthier and stronger as the season goes on, the Rockies look built for the long haul. That's a conclusion the Giants (28-18) came to long before Arenado crushed the game-winner off the left-field wall.

"It wasn't a surprise the kind of offense they've got, but they've really been pitching (well) too," Madison Bumgarner said. "They're starting to put it together. That's a really good team. It's not going to be an easy game when you're going out there facing them."

No night at Coors Field is a breeze, but Bumgarner and Rockies left-hander Franklin Morales fared about as well as you can normally expect. Both gave up three earned runs in six innings.

The Rockies struck first on two fourth-inning doubles, but the Giants bounced back with three runs in the top of the fifth, thanks in large part to a challenge by manager Bruce Bochy. With Brandon Crawford on first and one out, Tyler Colvin hit a slicing liner that appeared to nick the left-field line but was called foul. Bochy challenged, and the call was overturned, giving Colvin a double. Gregor Blanco's triple scored two runs, and he came home on an infield single by Hunter Pence.

The lead held up for just one inning. Wilin Rosario crushed a two-run homer in the sixth, and Bumgarner dug a deeper hole by walking Drew Stubbs and failing to get an out on a sacrifice bunt attempt by DJ LeMahieu. After a strikeout, Bumgarner stabbed Brandon Barnes' liner back to the mound and quickly threw to first for an inning-ending double play. Bumgarner set a franchise record with his 18th consecutive road start of three earned runs or fewer, but he wouldn't figure into the decision.

Colvin, who hit just .160 for the Rockies last season, sliced another double into left with Brandon Hicks on first in the top of the ninth, giving the Giants a 4-3 lead. Romo had converted 15 of his first 16 save opportunities, but he immediately ran into trouble.

A walk of Justin Morneau put the tying run on, and Romo narrowly escaped a walk-off when Michael Cuddyer's deep fly ball died on the right-field warning track. Troy Tulowitzki hit into a fielder's choice, erasing Morneau, and then went to third when Carlos Gonzalez lined a two-out, two-strike changeup inches over a leaping Brandon Crawford. Arenado smoked a hanging slider off the very top of the left-field wall, easily scoring the tying and winning runs.

Romo left the clubhouse before reporters entered, but Bochy said he didn't think his closer was that far off.

"It's a game of inches, and we just missed," Bochy said. "I thought we had a shot at Tulowitzki but just missed (a double play). The ball Gonzalez hit, I thought it might have nicked Crawford's glove. The last pitch (to Arenado) he just got up.

"It was a hard-fought game. It was a good game and obviously went down to the last pitch, two outs, two strikes. ..."

And a two-run double that shook Coors Field and firmly planted the Rockies in the race.

  • Buster Posey is listed as day-to-day with nerve irritation in his lower back, but the catcher was hopeful that he would be back behind the plate by the end of this three-game series. Posey suffered the injury during a funky swing in Sunday's game against the Miami Marlins and said his back stiffened up Monday. "I really don't think it's anything super serious," Posey said.

    The organization's actions spoke louder than words. The Giants considered calling up a third catcher, but Posey was cleared to back up Hector Sanchez on Tuesday and was available as a pinch hitter. Angel Pagan (sprained left shoulder) also was available off the bench after taking swings in an indoor batting cage. Pagan is expected to start Wednesday.

    The news was also good for right-hander Tim Hudson, who got the green light after throwing a bullpen session. Hudson missed his last start with a hip strain but will make his scheduled start in Thursday's series finale.

    For more on the Giants, see Alex Pavlovic's Giants Extra blog at blogs.mercurynews.com/Giants. Follow him on Twitter at twitter.com/AlexPavlovic.

    WEDNESDAY'S GAME
    Giants (Matt Cain 1-3) at Colorado (Jhoulys Chacin 0-2), 5:40 p.m. CSNBA