Despite a strong pitching performance from Tommy Milone -- who allowed just two runs on eight hits in seven innings while matching a career-high six strikeouts -- the A's squandered the few opportunities they did have to score.
Oakland loaded the bases in the first inning, a moment manager Bob Melvin referred to repeatedly throughout his postgame comments.
"I did feel like, especially in the first inning, we put some pressure on [Mazzaro]," Melvin said. "And a lot of times the first inning, when you get guys on base, is an inning where you can score multiple runs. And I really felt like we were going to, and we just didn't."
The A's best chance to get on the board came in the fifth inning. Adam Rosales drew a leadoff walk, and Collin Cowgill followed with a single. The runners moved up a base on Cliff Pennington's sacrifice bunt, before Josh Reddick lifted a fly ball, which left fielder Alex Gordon caught in foul territory. Rosales tagged from third, and Gordon's throw easily beat him to the plate. Rosales bowled over Royals catcher Brayan Pena, who held on to the ball for an inning-ending double play.
"The way we've been swinging the bats, to an extent, you have to take the opportunity to score a run right there," Melvin said. "But it was a heck of a play."
"We were trying to push the run across," Rosales said. "It was a great play by Gordon. I didn't see the throw, obviously. It was right on the money. It would've been nice to get that run. ... It had to be a perfect play, perfect catch, perfect throw. The catcher had to be in the perfect position. Everything went in their favor. Everything went right on that play for them."
"It was just a reaction play. I thought it was in the stands when he hit it and it crossed my mind, 'Should I catch it or let it drop?," Gordon said. "It was one of those bang-bang plays where I caught it, bobbled it and tried to chuck it over [Rosales'] head a little bit, and I put it right there. It was definitely a good time of the game for that to happen and we came out after that and scored a run, so it definitely gave us some momentum."
The A's had another opportunity in the eighth. The first two batters reached base, but after Yoenis Cespedes flied out, Kila Ka'aihue grounded into a double play to end the inning.
Milone pitched well enough to win on most days. Instead, he was hooked with the loss, lowering his record to 6-5.
"Milone pitched the way he's been pitching all year," Melvin said. "He got out of some jams a couple times, but you give up two runs, you should keep your team in the game and give them a chance to win. You expect to score at least two runs in a ballgame. I think he pitched according to form the way he has all year."
The Royals picked up their first run on a homer to straight-away center field from Eric Hosmer to lead off the the second inning.
"It was just a bad pitch," Milone said. "I'm trying to go away right there with a cutter and just left it right over the plate. That's where he hits his homers, right there, kind of middle in. I just kind of left it there for him."
Johnny Giavotella singled home Jarrod Dyson in the bottom of the fifth to bump the lead to 2-0.
The two runs were enough for Mazzaro, who pitched in 41 games over two seasons with Oakland.
"It's nice to get a start and go out there," Mazzaro said. "I wanted to attack the zone, put up the innings and get to our bullpen and get a win out of it -- and we did. It makes it a little better that it was against my former team."
The A's, after snapping a nine-game skid on Saturday, lost for the 10th time in their last 11 games.
"You've just got to keep battling through," Rosales said. "We all know it's a long season. Keep persevering, keep going forward. And we will. We have a lot of heart on this team, that I see, a lot of good attitudes."