PITTSBURGH -- Jeanmar Gomez thought he was going to spend Tuesday night in the bullpen, ready to come into the game early if struggling right-hander James McDonald faltered.
Instead, Gomez pitched five scoreless innings after being pressed into an emergency starting role when McDonald was scratched about two hours before the start of the game with right shoulder discomfort and placed on the 15-day disabled list.
Gomez allowed two hits and two walks while striking out five as Pittsburgh snapped an 11-game losing streak against the American League West with a 4-1 victory and handed Seattle just its fourth loss in its last 11 games.
"I came in like it was a normal day," Gomez said. "I'm doing my workout. That situation, you can't control, though, when they come and ask you to start."
He said it "was really hard" because he was a little tired from his workout, "but the manager asks me and I tell him I feel ready."
Gomez certainly looked ready as he shut down the Mariners.
"A guy comes in here at 4 o'clock and you tell him he's going to start, to get that effort we were real happy," Pirates manager Clint Hurdle said. "He continues to show up and do a very professional job in whatever we tell him to do. Tonight is a little bit above and beyond the call of duty."
The Pirates' last win over an AL West club came June 19, 2007, at Seattle. Yet the Mariners were no match for the 25-year-old Gomez.
"His stuff wasn't anything crazy, but he located his pitches well," Seattle second baseman Dustin Ackley said. "It doesn't really matter what kind of stuff you have if you move the ball in and out and up and down the way he did. It was a pretty good performance, especially for a guy who didn't know he was starting until a couple of hours before a game."
Pirates general manager Neal Huntington said McDonald told Pirates trainers after arriving at PNC Park that his shoulder was not feeling right. He was examined by team doctors and immediately put on the DL, though Huntington said it was too early to determine how long McDonald might be out.
Gomez (2-0) also made a spot start at Milwaukee last Wednesday and gave up three runs and four hits in four innings in place of Jonathan Sanchez, who had been designated for assignment a day earlier.
Huntington said Gomez would be a candidate to stay in the rotation. Gomez has primarily been pitching in long relief this season.
Andrew McCutchen went 4 for 4, accounting for more than half of the Pirates' seven hits. The center fielder is hitting .361 at home this season and .182 on the road.
"Andrew is in a good place right now," Hurdle said.
Garrett Jones added a two-run homer, a liner into the right-field stands, in the eighth off Carter Capps to push Pittsburgh's lead to 4-1. It was his fourth home run of the season.
"Their guy made a real good pitch and Carter didn't make a very good pitch," Mariners manager Eric Wedge said. "(If) it's a one-run game going to the ninth inning, then anything can happen. But a three-run deficit is pretty tough to overcome."
Jason Grilli pitched a 1-2-3 ninth and is a perfect 13 of 13 in save opportunities after entering the season with just five in his 10-year career.
Aaron Harang (1-4) pitched well in defeat, giving up two runs and five hits in six innings while striking out six and allowing no walks. Harang fell to 15-7 at PNC Park, where he has more wins than any other visiting pitcher.
Harang has allowed two runs in six innings in each of his last two starts after getting tagged for 16 runs in 12 2/3 innings in his first three starts after being acquired from Colorado.
"We've done our work trying to figure things out, and I've been where I need to be in these last two starts," Harang said.
The Mariners were held to five hits. Pinch-hitter Raul Ibanez drove in their only run with an eighth-inning double off Jose Contreras.
Pittsburgh broke on top with two runs in the first off Harang. Starling Marte reached on an infield single and Travis Snider and McCutchen hit consecutive run-scoring doubles to center field.
NOTES: Pittsburgh recalled utility player Josh Harrison from Triple-A Indianapolis to take McDonald's roster spot, and he struck out as a pinch-hitter in the fifth inning. His stay could be short as the Pirates figure to return to a 13-man pitching staff for Wednesday afternoon's game against the Mariners that wraps up the two-game series or Thursday night when they open a four-game series in New York against the Mets. ... Pirates catcher Russell Martin (strained neck) was a late scratch and is considered day to day. Michael McKenry took Martin's place. ... Pittsburgh second baseman Neil Walker (cut right index finger) will join Double-A Altoona for a rehab assignment on Thursday and then be evaluated after he plays two games. Walker could be activated as soon as Sunday in New York against the Mets. ... Seattle designated hitter Kendry Morales was out of the lineup because the DH rule was not in effect in an interleague game in a National League park. ... With Wedge forced to shuffle his lineup without a DH, third baseman Kyle Seager wound up batting third in the order for just the second time this season. ... Seattle will start Felix Hernandez (4-2, 1.60) in the series finale against Pittsburgh's A.J. Burnett (3-2, 2.57).