BOSTON -- When Roenis Elias was traded from the Seattle Mariners to the Red Sox this past December, his initial reaction was to make it work in Boston and win a championship.

On Friday night, the left-hander finally gets his chance to start to help his new team do just that.

And gets to do it against his old team.

Elias, acquired along with Carson Smith in the deal that sent Wade Miley to Boston, didn't make the Red Sox out of spring training and made one relief appearance with the big club on a call-up before going back and settling in at Triple-A Pawtucket.

Now, after a 4-0 record and 2.00 ERA in his last five starts, Elias joins the battle for Boston's fifth-starter spot vacated by Clay Buchholz and he faces former teammate Hisashi Iwakuma in the opener of a three-game series.

"This is someone who I think prior to the start of the season had made 40-plus (actually 49) starts at the big-league level so he might have been a little bit surprised that he didn't make our staff coming out of camp," manager John Farrell said before Thursday night's game. "He came up a couple of times and pitched out of the bullpen with some limited success but was back to a role he was most familiar with and that's a starting role and got on a little bit of a roll. So he handled that. I think that initial demotion, took a little time to get through but he's been on track.

"The work has been very good, the routines, more than anything have been consistent (and) he gets an opportunity here to run with it starting tomorrow."

Elias, 15-20 with a 3.97 ERA while with the Mariners, has limited the Triple-A opposition to a .194 batting average and struck out 40 while walking eight in the 36 innings over the last five starts. He did not allow a run in his last 13 innings.

He takes the mound after his new team dropped two of three to the Baltimore Orioles. The Red Sox had four hits during Thursday's 5-1 loss and are a game behind Baltimore for the American League East lead.

The Mariners snapped a four-game losing streak with a 5-4 win at Tampa Bay Thursday and Iwakuma (5-5) starts the series opener with four wins in his last five starts.

The right-hander is 0-1 with a 10.20 ERA in four career starts against the Red Sox, 0-0 with a 6.75 in two outings at Fenway Park. The Red Sox have 30 hits in 15 innings and have reached him for a .400 batting average. This will be his first start at Fenway since 2014.

Among the current Boston players, David Ortiz is 4-for-8 with two home runs and Dustin Pedroia 3-for-9 against Iwakuma.

Chris Iannetta went 3-for-4 and drove in a run as the Mariners set up their visit to Boston with their win in St. Petersburg.

"It's good to get a win, good to get a rally together," Iannetta said. "No matter what is being said or written, we're a tight unit, and we're going to keep playing that way."

The win gave the Mariners a 35-31 record and left them 6 1/2 games behind the Texas Rangers in the American League West and very much in the early wild card picture.