Reds third baseman Scott Rolen bobbled the short-hop, giving Arias enough time to beat the throw as the go-ahead run scored for a 2-1 victory Tuesday night that avoided an NL division series sweep.
Hardly able to get a hit the last two games, the Giants turned a passed ball and a misplayed grounder into a win that cut their series deficit to 2-1 and extended Cincinnati's 17 years of home postseason futility.
"These are the type of games we've played all season long," said Sergio Romo, who pitched the last two innings for the win. "We are a gritty and grinding team."
And, with their season on the line, a little lucky, too.
"We got a break there at the end," manager Bruce Bochy said.
Left-hander Barry Zito will pitch Game 4 on Wednesday for the Giants, who have won the last 11 times he started. The Reds have to decide whether to try ace Johnny Cueto, forced out of the opener in San Francisco on Saturday with spasms in his back and side.
Manager Dusty Baker said after the game that they hadn't decided whether to let Cueto try it, bring back Mat Latos on short rest again, or replace Cueto with Mike Leake, who wasn't on the division series roster.
Switching out Cueto would leave the Reds ace ineligible to pitch in the championship series should the Reds get that far.
"It's very difficult, but it all depends on if your ace can't go or whatever it is," Baker said. "That's part of the conversation -- us going without him. We realize what's at stake."
They were hoping to avoid having to make that choice. One grounder forced the issue.
The Giants managed only three hits against Homer Bailey and the Reds bullpen, but got two of them in the 10th -- along with a passed ball by Ryan Hanigan -- to pull it out. San Francisco won despite striking out 16 times.
Rolen, an eight-time Gold Glove winner, couldn't cleanly come up with Arias' grounder, which put him in a tough position.
"I've gone through the play many times in my mind between then and now, and I think I would play it the same way," Rolen said. "It hit my glove. I just couldn't get it to stick."
The Reds haven't won a home playoff game since 1995, the last time they reached the NL championship series. One win away from making it back there, they couldn't beat a Giants team that has barely been able to get a hit.
San Francisco got only two hits while losing 9-0 on Sunday night, setting up that 2-0 deficit in the series. The Giants had only one single in seven innings off Homer Bailey, making his first start at Great American Ball Park since his Sept. 28 no-hitter in Pittsburgh.
Fortunately for the Giants, Bailey's one lapse led to a run. He hit a batter, walked another and gave up a sacrifice fly by Angel Pagan in the third inning.
That was it until the 10th, with the Giants going down swinging -- the Reds set a season high with 16 strikeouts. Closer Aroldis Chapman got a pair of strikeouts on 100 mph fastballs during a perfect ninth inning, keeping it tied at 1.
San Francisco's one-hit wonders finally got it going against Jonathan Broxton, who gave up leadoff singles by Buster Posey -- the NL batting champion -- and Hunter Pence, who pulled his left calf on a wild swing before getting his hit.
With two outs, Hanigan couldn't come up with a pitch, letting the runners advance. Moments later, Cincinnati's chance for a sweep was over.
Instead, a Reds team that lost a lot -- closer Ryan Madson in spring training, top hitter Joey Votto for six weeks at midseason, Baker for the NL Central clincher, Cueto in the first inning of the first playoff game -- ended up with another playoff loss at home.
Baker was back in the home dugout at Great American for the first time in nearly a month, recovered from an irregular heartbeat and a mini-stroke. After a pregame ovation, he settled in his red folding chair with a toothpick on his lips.
The 63-year-old manager watched his pitching staff dominate again, but fail to get that breakthrough win. This time, the offense came up short, getting only four hits.
Cincinnati hasn't won a home playoff game since beating the Dodgers 10-1 at Riverfront Stadium for a three-game division sweep in the 1995 NLDS. They then got swept by Atlanta.
They didn't get back to the playoffs again until 2010, when they got no-hit by Roy Halladay and swept by the Phillies in the opening round.
The second-largest crowd in Great American history was still getting the hang of playoff rooting. A video board message instructed the 44,501 fans not to wave white rally towels while the Reds were in the field -- could be distracting.
Didn't take long to get those towels twirling. Brandon Phillips led off with a single, but was thrown out at third when he tried to advance on a ball that got away from Posey. It was costly -- the Reds went on to score on a walk and a pair of singles, including Jay Bruce's RBI hit to right.
The Reds got only one more hit the rest of the way.
NOTES: The game started 3 minutes late because a sign-waving fan ran onto the field. He was tackled by police in center field. ... Giants avoided their third playoff sweep in franchise history. ... The Giants haven't lost three in a row since they dropped five straight from July 25-30. ... Tom Browning, who pitched the Reds' previous no-hitter -- a perfect game against the Dodgers in 1988 -- threw the ceremonial pitch. ... Bailey fanned six in a row, matching the Reds' postseason record. ... The only larger crowd at GABP was for the 2010 playoff game against Philadelphia.