KANSAS CITY -- It was all going so well for Frankie Montas. And then, suddenly and decisively, it wasn’t.

The A’s had to feel great about their chances in the third inning Tuesday, as Montas -- who had been on a roll over the past few weeks -- was staked to a six-run lead. But the Oakland right-hander couldn’t keep the Royals under control and wound up being pulled after just 3 1/3 innings, tagged with more than three runs for the first time in a start since June.

Thus, an already stressed Oakland bullpen had too many innings to cover and Kansas City roared back for a 10-7 victory in the A's third straight loss -- and the latest in a series of gut punches to their postseason aspirations.

Montas came into the game 3-0 with a 1.30 earned run average over his previous four starts. But the Royals kept pounding out hits, trimming their deficit in half before Montas concluded the third. Reliever Deolis Guerra stopped the surge temporarily in the fourth after Montas departed, but the Royals would eventually take an 8-7 lead in the sixth on Salvador Perez’s towering three-run homer off Yusmeiro Petit, tacking on two more and holding on for the win starting Oakland's road trip on a tough note.

Montas gave up eight hits and was charged with four runs while recording just 10 outs. It was a far cry from his previous six outings, a span that saw him allow just eight earned runs over 38 2/3 innings. Given their standing in the AL Wild Card race -- the A's entered Tuesday 2 1/2 games out of the second spot -- they can ill afford to blow a six-run lead with one of their most reliable starters on the mound if they hope to reach the postseason for the fourth straight season.

“His stuff was good. He was just throwing some balls down the middle, I think,” manager Bob Melvin said of Montas. “It’s tough to tell from our angle, but wasn't giving up multiple swings in a row that are good swings. You are going to have games like that. But certainly the way he started, it looked like he had really good stuff.”

Montas pointed to the fact that the A’s (77-67) still have 18 games left, adding that he expects the club to show a lot of fight and finish with a bang. 

“None of us feel good about the game today,” Montas said. “But we can’t get stuck on one game. We have to keep moving forward and keep trying to win ball games.”

For Yusmeiro Petit, one of Melvin's most utilized and trusted relievers, the big damage on the night came when Perez put the Royals ahead with his a three-run homer in the sixth, symbolizing the plight of the Oakland bullpen in recent weeks.

“We’re battling,” Petit said. “It’s a tough week for us, but we fight every day.”

The Kansas City bullpen outdueled the A’s bullpen by allowing just one run after the third -- and no base hits after the fifth. Once Perez put Kansas City ahead, the Royals’ relievers took it from there.

“We’re still grinding,” Melvin said. “We talk every day and we know where we are. We’ve had some tough games along the way in the last couple of weeks. Everybody knows where we are. We have to go out there tomorrow like it’s the last game we’re playing.”