"We're either going to have to get really hot real here soon, or a couple of teams in our division have to get really cold," said Arroyo, referring to the National League Central's top two teams in the Pirates and Cardinals.
Third-place Cincinnati, which entered the day 3 1/2 games behind Pittsburgh, has a 35-12 record vs. sub-.500 clubs and are 30-16 at Great American Ball Park. The Reds came into the series winners of three straight games vs. the Giants.
Those records should have played in their favor, but the young Mariners -- who had just beaten the Rangers at Texas in two of three games -- clearly had different plans.
"I think they played good. I think we didn't play to our capabilities," third baseman Todd Frazier said. "We have to put more runs up, especially against the guy we faced in [Joe] Saunders that's not overpowering. We have to find a way to win that game. This is one you look back on, just confused and just wondering what we could have done to win."
Arroyo had a quality start, as he gave up three runs and five hits, including two home runs, over his six innings, with one walk and six strikeouts.
For the third straight game, the Mariners -- who had eight lefties or switch-hitters in the lineup against Arroyo -- used a first-inning home run to jump out in front quickly. This time, it was No. 2 batter Nick Franklin who hit a solo homer to right field on a 1-2 pitch. Seattle has a Major League-best 22 first-inning home runs this season.
"You can't just lay it in there against guys you don't know anything about," Reds manager Dusty Baker said. "After you learn something about them -- they've already homered off of you. They've got a good, young bunch of guys. They're going to be something to deal with in the next couple of years."
In the third inning, following a Kyle Seager one-out walk, Justin Smoak sent a first-pitch offering into the left-field seats for a two-out, two-run homer and a three-run Seattle lead.
The long balls marked homers Nos. 235 and 236 hit against Arroyo with the Reds, which broke the all-time club record held by Tom Browning. Of course, Browning never pitched in homer-happy Great American Ball Park.
"You take every home run I've ever given up in this ballpark and stick me in San Francisco, maybe I only give up two-thirds of them," Arroyo said. "That's life here. It obviously swings both ways so you can't be so disappointed by it."
Arroyo retired the next nine in a row and 10 of his final 11 batters. Unlike the Reds' 13-4 win over the Mariners on Saturday, there was little in the way of offensive cavalry to take back the game.
"I was never really in a groove today," Arroyo said. "It was just a hard-fought battle for me. Eight left-handed guys, I didn't have the sharpest of stuff. I was having to throw a lot of max-effort pitches. I knew we were down three already and the flow of the game wasn't feeling conducive to us putting four on the board any time soon. I was taking every inning like it was do-or-die for me just to give us an opportunity to come back in the ballgame."
Saunders, who came in 0-2 with a 6.04 ERA in four career starts vs. the Reds, pitched seven innings with six hits allowed. He kept Cincinnati scoreless until the seventh.
The Reds hit three first-inning singles and still came away scoreless. Shin-Soo Choo was promptly erased following a leadoff single when Zack Cozart grounded into a double play. Singles by Joey Votto and Brandon Phillips followed before Jay Bruce grounded into a fielder's choice to end the inning -- the first of 11 in a row retired by Saunders and 16 of 17.
"I thought we'd manage more than one run off of him," Baker said. "We were very satisfied with the job Bronson gave us. Three runs, especially off of that total left-handed lineup."
There was one out in the Reds' seventh when Frazier laced a double to the wall in right-center field and scored on next batter Chris Heisey's second double of the game, a liner towards the left-field corner. Heisey was left stranded when Ryan Hanigan and pinch-hitter Derrick Robinson grounded out.
"I think it definitely hurts a bit," Arroyo said of the series outcome. "It's getting to that point in the season where you're starting to see the numbers stack up. Your ERA and batting average settle in now. You're getting enough at-bats, enough innings where things aren't going to move too much. It gets harder to make moves. It's starting to get to that point in the standings as well."