For the first five innings, Pittsburgh farmhand Gerrit Cole was on cruise control.

Then things started to come unglued in the sixth, and what started out so promising left baseball's No. 8 prospect with a sour taste of deja vu.

Cole (3-5) struck out a career-high nine batters while allowing two runs -- one earned -- on three hits over six innings, but the Double-A Altoona Curve fell to the host Portland Sea Dogs, 2-1, on Thursday evening.

Cole's previous high was seven strikeouts. He achieved that three times, most recently with the Class A Advanced Bradenton Marauders, in a 6-0 win over Fort Myers on June 14, his final start in the Florida State League.

"There are a lot of positives, but there's obviously a lot of things to work on," said Cole, who threw 91 pitches. "It was pretty bittersweet. I got through five innings, then handed them the lead back in the sixth."

To steal a soccer cliche, Cole's outing was a game of two halves.

The top pick from the 2011 Draft retired the first 14 batters he faced, allowing just one ball to leave the infield. Hot-hitting Xander Bogaerts broke up his perfect-game bid with a two-out double to right field with two outs in the fifth, but Cole induced an inning-ending ground ball off Peter Hissey to preserve the 1-0 advantage.

"It was the first curveball I had thrown the whole night," Cole said of Bogaerts' hit. "It was 80 mph and I tried to get it in there for a strike, but I ran the risk of letting him get the bat head out on it. A lot of people would roll over it, but he did a good job of going the other way.

"My fastball location was good and I was changing speeds when I needed to. They weren't really doing too much at all, maybe two or three balls out of the infield. I could have used another strikeout in the sixth [inning], but the chips fell where they did."

In that frame, the UCLA alum was unable to keep the Sea Dogs at bay. Christian Vazquez led off with a grounder to left field, and Jackie Bradley hit a ball off the glove of charging shortstop Oscar Tejada and into right-center field, advancing to second on the miscue.

Marquez Smith then tied the game on a run-scoring groundout, and Bradley scampered home with what proved to be the eventual winning run on a pitch in the dirt that veered away from catcher Ramon Cabrera.

"It's frustrating. The ground ball was hit real soft and the pitch in the dirt was where I wanted to throw it, but it took a weird hop and the catcher couldn't do anything about it," the 6-foot-4 right-hander said.

"I wasn't tired, I was still throwing 100 mph in the sixth, but I don't know. I don't have an answer. This is the third time that I couldn't get out off my last inning. I need to do better, no excuses. It's not acceptable and I'm better than that. I'll just have to figure it out next time."

With the loss, Pittsburgh's No. 2 prospect behind Jameson Taillon fell to 3-5 in the Eastern League and 8-6 overall.

The 21-year-old California native went 5-1 with a 2.55 ERA in 13 starts with the Marauders before his promotion to Altoona in mid-June. Across the two levels, Cole has a 2.82 ERA with 121 strikeouts over 115 innings, and he has held opponents to a .224 batting average.

"Things are going well. I'm learning a lot and just getting used to the flow of things," he said. "I'm sure there are bunches of people whose expectations I'll never fill, but my goal is to get better every time, and for the most part, I've executed that quite well."