PAWTUCKET –– Pitcher Michael Bowden is such a highly touted prospect that every hot streak makes many believe that he's ready for the big leagues, while every bump in the road brings just as many fears that he'll never make it.

The No. 2-ranked prospect in the Boston system has had plenty of both this year –– a tremendous hot streak to begin the season and a rocky patch of late, giving him a somewhere-in-the-middle 3.38 ERA for the season. Monday night, Bowden gave up four runs in 4 2/3 innings, though he kept his team in the game long enough for them to win in extra innings.

But Bowden's recent difficulties may actually mask a fundamental improvement. Bowden has been working to incorporate a slider into his repertoire with the hope of giving the contact-oriented command pitcher a true "out pitch" that will let him rack up the strikeouts.

"I think it's going to define him. I really do," said Pawtucket pitching coach Rich Sauveur. "I honestly think that pitch is going to define him, to help him get back to where he wants to be."

As Bowden makes that pitch more a part of his arsenal, he has needed to adapt and the adjustment has come during a time when he has suffered through some fluke performances and made some mistake pitches at the wrong times.

"I was throwing the ball well, I was hitting my spots well. I left a few pitches up at critical times in the game, and they capitalized on them," Bowden said.

Sauveur was only really unhappy with an 0-and-2 changeup that Bowden threw over the plate. The hope is, with the slider to fall back on as an out pitch, there won't be a need to throw an 0-and-2 changeup for a strike ever again.

Bowden rolled into the end of May with an ERA under 1.00. From that point on, he has been spotty at best, alternating between good starts and poor ones. His ERA since May 23 is 6.42.

But his only really poor outing since early June was a six-run, one-inning disaster in Durham on June 19. Bowden chalked that up to feeling downright strange –– heat exhaustion in the 96-degree North Carolina humidity, he said.

He looked at the Durham outing as the exception, not the rule, he said, and believes he's pitching well of late.

"I feel good. The outing in Durham, that heat kind of caught me off guard," Bowden said. "I haven't pitched in those conditions all year. I had absolutely no energy. I had a little heat exhaustion. I couldn't even throw a strike. I've never felt like that, really."

Coming into Monday night, Bowden had allowed two runs or less in three of his last four outings, with Durham the exception.

In that game, Bowden threw about 10 sliders and plans to incorporate the pitch even more. He had been working on the pitch most of the year, but it has become a useful pitch only in his last two outings. Before that, Bowden couldn't throw it with any break, or for a strike.

"It was either straight or it was buried in the ground and they thought it was a changeup.

He'd throw one strike with it a game, so it wasn't even a thought," Sauveur said.

Now, it will give the fastball-curveball-changeup pitcher another weapon to keep hitters off guard. The slider comes in between 83 and 87 mph, a perfect complement to his 92-mph fastball and his roughly 80-mph curve.

"Just over the past two outings, it's improved a ton. It's an out-pitch for him, and he throws it for strikes. I'm very impressed with that," Sauveur said. "Now, every game, these guys who have seen him before, it's going to be, 'What the heck was that?' "

dbarbari@projo.com