The Orioles will send their hottest pitcher – left-hander Brian Matusz – to the mound tonight with the opportunity to sweep the Red Sox at Fenway Park.

Yes, Matusz, who entered the season possessing the longest personal losing streak in baseball, seems to have things figured out of late.

Matusz (5-5), who is going for his fifth win in his past six starts, is 4-1 with a 2.78 ERA and he’s coming off his best outing of the season, a season-high 7 1/3-inning start at Tampa Bay in which he allowed just two hits and one run while striking out seven. His outing Saturday was his longest in nearly 22 months, when he threw eight innings against the Rangers on Aug. 19, 2010.

The 25-year-old left-hander is also using his pitches effectively. Despite issuing three walks Saturday, he didn’t labor deep into counts, allowing his 97 pitches get him into the eighth inning.

He’s using his slider effectively – 22 of his 29 sliders were strikes in his last outing -- especially a backdoor slider that starts outside to right-handed hitters then enters the zone at the last minute.

Rays hitters swung at his slider 19 times and missed 10 times for a 52.6 swing-and-miss percentage (compared to a 29 percentage on the season).

“It’s been really big for me, especially since my change-up has been a little inconsistent, so to be able to have that, it’s been nice,” Matusz said. “It’s just throwing them in the right count. I don’t know how many of those sliders were down out of the zone, that started as strikes and ended up being down. It’s just depending on the situation and the count and where I want to go with it.”

Orioles pitching coach Rick Adair said Matusz showed a lot of confidence using his backdoor slider as an out pitch. Adair has also been impressed with Matusz’s ability to throw the sliders at different speeds, with his slider that starts over the plate and breaks down and in to right-handed batters coming in with more velocity.

“He’s done a tremendous job with that,” Adair said.

Getting a feel for his breaking pitches has also allowed Matusz to get more ground ball outs. Over his past five starts, he owns an impressive 1.04 groundball-to-flyball ratio.

Here’s a breakdown of Matusz’ groundball-to-flyball ratio. Over his past five starts, a span in which he’s gone 4-1 with a 2.79 ERA, he has a 1.04 ratio.

2012 (Last five starts) 47/45 1.04

2012 (First six starts) 34/79 0.43

2011 51/129  0.39

2010 205/339 0.58