OAKLAND -- It’s tough to gauge what type of pitcher the A’s have in Frankie Montas.

Some nights, Montas will carry a dominance on the mound that's on par with the best pitchers in the game. Other times, sudden lapses of command can lead to struggles with keeping the ball in the yard. A mix of those two sides to Montas was present in Monday’s 4-2 loss to the Mariners, as the right-hander recorded a season-high 11 strikeouts while also giving up all four runs.

“Sometimes you make mistakes that you get away with, and sometimes you don’t,” A’s manager Bob Melvin said. “Today, he didn’t get away with his mistakes.”

Two homers allowed were the costly mistakes made by Montas that ultimately made the difference in Monday’s outcome. He surrendered a two-run shot to Kyle Lewis in the third and a solo shot to Jarred Kelenic in the fifth. Susceptibility to the long ball continues to be Montas’ biggest obstacle. The two homers against him on Monday brought his season total to 11, which sets a new career high.

Though both homers came on fastballs, it was the offering to Lewis that truly left Montas displeased, especially knowing the Mariners slugger’s tendency to pounce on fastballs. After getting ahead in the count, 1-2, with three straight sliders, Montas left a 96.9 mph heater over the heart of the zone that was deposited well up the Coliseum’s bleachers in left-center field.

“I made a mistake on the fastball to Lewis,” Montas said. “He’s always jumping on the fastball. I made that mistake and he made me pay the price.”

Even in defeat, Montas displayed the tantalizing stuff that continues to give the A’s hope that he could put it all together soon. Of his 11 strikeouts, eight were of the swinging variety. He also recorded a career-high 21 whiffs, with 11 coming on his splitter.

The splitter, used as the putaway pitch on six of the punchouts, was the main ingredient in producing the fourth double-digit strikeout performance of his career. Combined with a power sinker that maxed out at 97.9 mph on Monday, Montas should see better days if he can get the home runs under control. For now, he sits at 5-4 with an ERA that ticked up to 4.92.

“He had a really good split tonight,” Melvin said. “Really, just two fastballs in the middle of the plate ended up being three of the four runs.

“Some deep lineups throughout the league, when you make mistakes, they’re hitting homers. I know that was the case tonight.”

Montas still managed to leave the A’s within striking distance by the time he departed. Right-hander Cam Bedrosian, who came on in relief of Montas for his A’s debut, kept Oakland close by retiring six of the seven batters he faced over two scoreless innings. But on a cold night in Oakland, the bats cooled off.

Coming off a three-game series against the Angels in which they clubbed nine homers, the A’s struggled to piece together any serious rallies against Mariners left-hander Yusei Kikuchi. Mark Canha’s solo homer in the third was the only production for most of the night until Seth Brown cut the deficit to two runs with a pinch-hit RBI double in the eighth.

Despite only collecting five hits, the opportunities were there for the A’s late -- they just didn't capitalize. The most notable situation was in the eighth, when the A’s had runners on first and second with no outs following Brown’s double and a walk by Canha. Seattle’s Erik Swanson, however, struck out Chad Pinder, Ramón Laureano and Matt Olson to end the threat.

“I think it was their pitching tonight. They pitched well,” Melvin said. “In general, it’s a little more difficult to hit home runs here at night. Canha hit one out to right field tonight, which is tough to do. But they pitched us well tonight.”