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Rookie right-hander Gerrit Cole makes his fourth start for the streaking Pittsburgh Pirates on Friday when they host the Milwaukee Brewers in the opener of a three-game series at PNC Park.

The 22-year-old was a first-round pick of the New York Yankees -- 28th overall -- out of high school in 2008, but did not sign. He was then selected first overall by the Pirates in 2011.

He rose through three levels of the minor leagues in 2012 while going 9-7 in 26 starts with a 2.80 earned run average. He then opened 2013 with Triple-A Indianapolis and won five of eight decisions in 12 starts.

Cole made his big-league debut on June 11 against San Francisco while allowing two runs in 6 1/3 innings of an 8-2 defeat of the Giants.

In two subsequent starts against the Los Angeles Dodgers and the Los Angeles Angels of Anaheim on June 16 and 21, he combined to surrender 11 hits and five runs in 12 innings of work.

For the Brewers, towering right-hander Johnny Hellweg makes his big-league debut after 148 games in the minors.

The 6-foot-9, 205-pounder was drafted in the 16th round by the Angels in 2008 and was with the Angels organization until the 2012 trade that sent Zack Greinke from Milwaukee.

He was 7-11 in 28 appearances at Double-A in 2012 and went 7-4 in 14 starts at Triple-A Nashville this season.

He's getting the start in place of Alfredo Figaro, who went on the disabled list with a strained right oblique.

On Wednesday in Milwaukee, Anthony Rizzo went 2-for-4 with a double and two RBI to lead the Chicago Cubs to a 5-4 win over the Brewers.

Aramis Ramirez went 2-for-4 with a homer and two RBI and Juan Francisco added a solo shot for the Brewers, who had won three of four entering the contest.

Yovani Gallardo (6-7) gave up five runs -- three earned -- on eight hits and four walks over four innings to absorb the loss.

In Seattle, Jordy Mercer's go-ahead RBI single in the top of the ninth inning lifted the Pirates to their sixth straight victory, a 4-2 decision over the Mariners in the finale of a two-game interleague set at Safeco Field.

With two runners on, Mercer ripped a two-out single back up the middle against Yoervis Medina to put the Pirates in front. Travis Snider then scored an insurance run when Medina's strikeout of Starling Marte went for a wild pitch.

Neil Walker had two hits and slugged a two-run homer for the Pirates, who swept the West Coast part of the nine-game trip to finish the trek with a 7-2 record. They took all three from the Angels prior to their set with Seattle.

Vin Mazzaro (4-2) tossed a pair of scoreless innings and Mark Melancon worked around two hits in the ninth to record his second save.

Jeanmar Gomez returned from a stint on the disabled list to throw five strong innings for Pittsburgh. In his first start since June 2, he struck out five and limited the Mariners to one unearned run on three hits.

"He gave us the innings we needed," said Pirates manager Clint Hurdle. "He was effective again, real nice job."

The Pirates won six of the first 10 games between the teams in 2013, while the Brewers won 11 of 15 in 2012.