BOSTON -- For Red Sox pitcher Edward Mujica on Saturday night, the excitement he showed on the field after getting the last out of the game said it all.

A day after being named the team's closer with Koji Uehara struggling mightily over the past several weeks, Mujica's first shot at a save opportunity in his new role came Saturday against the Toronto Blue Jays with a runner on first and one out in a 4-3 game. Mujica was able to preserve the lead, sandwiching a walk between two outs and showing off an emphatic fist pump as he nailed down his first save since Aug. 13.

In his first save opportunity since replacing Koji Uehara as closer, Edward Mujica got it done, finishing off the Blue Jays. AP Photo/Winslow Townson

"It's good," Mujica said of the save. "When I signed here they told me, 'You're going to be in the back of the bullpen backing up Koji.' They gave me the opportunity earlier in the season and now I'm just trying to pick up Koji because he's been having rough outings."

For now, Mujica is no longer just a backup to Uehara. Although Farrell said Friday that ninth-inning duties will most likely be handed back to Uehara before season's end, Mujica finds himself in strong position to prove he can be the go-to guy.

And don't let his overall numbers this season fool you. As bloated as his 4.00 ERA may seem for a closer-type, Mujica has pitched much more effectively since a horrifying April that saw him give up 10 runs on 14 hits in nine innings pitched (10.00 ERA).

In fact, he's been dominant at times over the last five months, putting together a streak of 14 straight outings without allowing an earned run from July 27 to Aug. 22 and posting an ERA of 2.78 in 45 1/3 innings since the start of May.

"When I got here they told me they don't want to use me a lot because I pitched a lot last season [with St. Louis]," Mujica said. "Spring training, I think I got like five, six innings only of work. I think April was like tricky for me because I think I need a little bit more work in spring training to get ready for the season. Things can happen, I'm just trying to work hard every single day and get ready."

On Saturday night, Mujica had extra time to get ready for his appearance as Red Sox manager John Farrell stuck with left-handed reliever Drake Britton entering the ninth with Toronto lefties Colby Rasmus and Munenori Kawasaki due up. Britton was able to punch out Rasmus swinging on a 3-2 curveball before losing Kawasaki on ball four and turning things over to Mujica to finish the job. The outing was Britton's second in two days since rejoining the team Friday.

"I'd like to see him continue what he's doing," Farrell said. "This year in Pawtucket might not have been his strongest year but don't lose sight of what he did for us last year at the major league level. He's been durable, he's resilient, he's got good stuff. Any opportunity anybody has here for us is going to be an evaluation period for anyone."

Just as general manager Ben Cherington and Farrell said at the trading deadline, the rest of this season primarily remains an evaluation period for the Red Sox. Much has been made about the influx of new faces into the starting rotation after the departure of Jon Lester, John Lackey and Jake Peavy, while the offense is starting to thrive with the likes of Yoenis Cespedes, Mookie Betts and a reinvigorated Xander Bogaerts.

But don't be so quick to overlook the bullpen. With Craig Breslow, who gave up a two-run home run to Rasmus in the seventh inning on Saturday, continuing to struggle and the Sox holding a team option on him for 2015, seemingly every role in the pen is up for grabs. There's still much to be proven among the Red Sox relief corps the rest of this month.

No matter what happens the rest of the way, Uehara is a free agent after this season. So for Mujica, who's under guaranteed contract with the Red Sox for 2015, the pressure is on to perform well.

"The opportunity is there," Mujica said. "This is a big opportunity for me to go out there and show what I can do."

Would he consider it an audition for the 2015 closer role?

"I don't know,' Mujica said. "They [make] that decision. I have to go out there and just work."