SAN FRANCISCO (AP) — Two weeks ago the Arizona Diamondbacks seemed a lock to make it to the postseason. Now just finishing the year with a .500 record may be a struggle.

One day after losing to San Francisco in the ninth inning, the Diamondbacks let another game slip away in the final at-bat when Eugenio Velez hit a two-out, two-run triple off Arizona's Brandon Lyon to lift the Giants to a 4-3 win on Wednesday. It was the second straight walkoff hit for Velez and completed San Francisco's three-game sweep. It also sent the slumping Diamondbacks to their sixth straight loss overall and 10th consecutive on the road to fall three games behind the Los Angeles Dodgers in the NL West. Los Angeles plays at San Diego later Wednesday.

"That's the way it's going right now but it's to the point where sulking and getting down and pressing ... it's time to put an end to that stuff," Arizona catcher Chris Snyder said. "It's time to just go all out, play your hardest, lay your chips on the table and see what happens."

Not much has gone right for the Diamondbacks lately.

Arizona held a 4_ game lead over the Dodgers on Aug. 29 but has lost nine of 11 since then to fall to a season-high three games below .500 at 71-74. With at least five teams ahead of them in the chase for the wild card spot, the Diamondbacks' hopes of making the playoffs are fading fast. They finished their road trip 0-6 and haven't won on the road since beating Houston 11-5 on Aug. 16. Arizona plays 10 of its final 17 games at Chase Field but has a final seven-game trip to Colorado and St. Louis later this month.

"It's just weird how things are going but at the same time we can't give up on ourselves," said center fielder Chris Young, whose two-run triple off San Francisco closer Brian Wilson in the top of the ninth gave Arizona a brief 3-2 lead. "It was a horrible road trip, no question about that. But we aren't going to give up. No matter what people expect we're going to still go out there and fight every day. That's all we can do."

The Diamondbacks might have fared better were it not for Velez. The Giants' infielder drove in the game-winning run in the ninth inning of Tuesday's 5-4 win over Arizona and knocked in San Francisco's first two runs off Diamondbacks starter Dan Haren on Wednesday.

Velez was down 0-2 to Lyon (2-5) when he drilled a fastball to the gap in right-center, scoring pinch-runner Ryan Rohlinger and Aaron Rowand as the afternoon crowd at AT&T Park roared.

"In that situation always I'm looking for a fastball," Velez said. "I'm a fastball hitter so I don't want to swing at something soft and hit a groundball or something like that. If I get a fastball in that situation with two strikes, I have to swing. I was waiting for it."

The Giants matched their season-high win streak of five straight.

Alex Hinshaw (2-1) got one out for the win after Wilson blew his fifth save of the year. Wilson, second in the NL with 37 saves, stood to take the loss before his teammates rallied off Lyon.

Bengie Molina started the comeback with a one-out single. Rohlinger entered to pinch run and moved to second when Rowand walked with two outs before Velez came through with his second straight game-winning hit.

"Same guy, same hero," Giants manager Bruce Bochy said. "He's a battler, I'll say that. He's still in the learning stage about the game ... but he's got great tools. He's done the things you want to see."

Young's two-run triple off Wilson prevented San Francisco starter Brad Hennessey from claiming his first win in more than two years but wasn't enough to keep San Francisco from sweeping the Diamondbacks at AT&T Park for the first time since April 20-22, 2007.

Hennessey, who was taking Kevin Correia's turn in the Giants' rotation, made his first start since Sept. 15, 2006. The righty spent the better part of two years in the bullpen but pitched well in a series of starts in the minors, convincing Bochy to use him against the Diamondbacks.

The plan worked better than expected until Arizona rallied against Wilson.

Hennessey pitched six strong innings, giving up four hits including a solo home run to Stephen Drew in the third, and pitched out of jams in the first and fourth. He retired nine of the final 11 batters he faced before giving way to reliever Jack Taschner to start the seventh.

That seemed to be enough against Arizona, which hadn't shown much life the past two weeks while tumbling out of first place in the NL West.

"We just couldn't finish it off," Diamondbacks manager Bob Melvin said. "It's the same as we were yesterday. We've just got to find a way to win some games, get one under our belt and hopefully roll off of that."

Drew homered off Hennessey in the third but the Diamondbacks couldn't get much else off the Giants' starter, who left with a 2-1 lead after Velez's bases-loaded double in the third.

Haren lasted only four innings to run his winless streak to four straight starts.<