Hernandez (5-2) struck out five and walked one to improve to 4-0 in his last five starts while shaving his ERA to 1.53. The right-hander shook off a shaky first inning then settled down to allow four base runners in his final seven innings of work. Tom Wilhelmsen worked the ninth for his ninth save.
Burnett (3-3) was almost as sharp, giving up just two hits over seven innings while striking out nine. Yet he also walked four batters and gave up Montero's third homer of the season with one out in the seventh.
Starling Marte had two hits for Pittsburgh and Andrew McCutchen added an RBI single but the Pirates couldn't sweep the brief two-game series.
The showdown between the two staff aces lived up to its billing. Hernandez entered the game ranked in the top five in the American League in ERA and strikeouts while Burnett came in unbeaten in nearly a month and second in the National League in strikeouts behind New York's Matt Harvey.
Hernandez's only miscue came in the first. Starling Marte led off with a double - his 17th lead-off hit this season - then came around to score when McCutchen singled up the middle with one out. Garrett Jones then walked, but Pittsburgh's promising inning disappeared when Mike McKenry hit into a double-play.
It was the fourth straight game in which the Pirates let a potentially big first inning slip away.
And Hernandez didn't botch his reprieve. Pittsburgh only managed to get one runner to third the rest of the way. Jordy Mercer doubled leading off the fifth and advanced to third with one out. Burnett, however, couldn't square a sacrifice bunt and Marte struck out.
Burnett cruised through the first three innings, needing an economical 32 pitches to retire the first nine batters. Yet his control briefly abandoned him in the fourth and his unfamiliarity with backup catcher McKenry may have cost the Pirates a run.
Michael Saunders and Jason Bay walked leading off the fourth and were on second and third with two outs when Burnett bounced a curveball to home plate that smacked off McKenry - who was catching Burnett for just the second time in the regular season due to an neck injury to starter Russell Martin - and rolled away, allowing Saunders to race home and tie the game.
Burnett had little trouble with one of the worst offenses in the majors until the seventh, when Montero took a 91 mph fastball and put it in the first row of seats in center. Hernandez and Wilhelmsen took care of the rest as the Mariners improved to 8-4 in their last 12 games as they try to bounce back from a horrific start.
NOTES: The Pirates released RHP Jonathan Sanchez on Wednesday. The team designated him for assignment last week ... The Mariners are off on Thursday then host Oakland for a weekend series starting Friday. Hisashi Iwakuma (3-1, 1.61) starts for Seattle against Dan Straily (1-0, 5.94) ... Pittsburgh begins a four-game set in New York against the Mets on Thursday. Jeff Locke (3-1, 3.21) faces New York's Dillon Gee (2-4, 6.16) ... The Pirates called up 2007 second-round pick RHP Duke Welker on Wednesday. Welker was 3-0 with a 0.00 ERA at Triple-A Indianapolis this season.