Hernandez struck out 10 in seven innings and left with the score tied 1-all. It was his 13th consecutive start with at least seven innings and no more than two runs allowed, matching Tom Seaver's major league mark set for the New York Mets in 1971.
Chief Bender held the previous AL record of 12 in a row established in 1907.
Kendrys Morales had a sacrifice fly in his first game back with the Mariners, who have lost four straight and are 2-6 since the All-Star break.
Left fielder Steve Pearce threw out a runner at the plate for Baltimore, which remained three games in front of the second-place New York Yankees in the AL East.
Davis sent a 1-2 pitch from Charlie Furbush (1-5) into the right-field seats for his 17th home run.
Cruz connected off Hernandez in the second for his 29th of the season, keeping him one behind Chicago White Sox rookie Jose Abreu for the big league lead.
Abreu hit No. 30 on Friday night in a victory over Minnesota.
Darren O'Day (3-1) worked the ninth and Zach Britton earned his 19th save in 22 opportunities. Baltimore won an instant replay review for the final out.
Hernandez gave up five hits and walked none. He is 7-1 with a 1.36 ERA, 113 strikeouts and 17 walks during his last 13 starts.
The Mariners had a series of chances, but Orioles starter Kevin Gausman consistently threw the right pitch to work out of most trouble.
Seattle advanced a runner to third with two outs in the first, third and fourth. Endy Chavez was pinned there in the first inning when Kyle Seager struck out. Brad Miller reached third in the third, but Robinson Cano bounced out to first. Seager was stranded in the fourth when Logan Morrison struck out.
Then in the fifth, it appeared the Mariners had something going after Miller's one-out walk. Chavez grounded a ball through the right side, with Miller racing to third. However, the umpires ruled immediately that the ball ticked off Miller's shoe. He was ruled out and Chavez was credited with a single.
Chavez stole second and James Jones lined a single to left. Chavez tried to score, but was thrown out easily by Pearce.
Seattle finally broke through in the sixth. Cano opened with a triple into the right-field corner. Morales, in his first game since Thursday's trade with Minnesota, lifted a sacrifice fly to right. Cano made a nifty, left-handed sweep of the plate to avoid the tag.
Cruz's first-pitch solo shot in the second curled into the left-field corner, clearing the wall by not much more than a yard as Hernandez flashed an incredulous look.
Hernandez had been among the toughest pitchers to take deep. He had allowed five home runs this season, just two in his previous 16 starts.
The Orioles have 125 home runs, matching Toronto for most in the majors.
NOTES: Orioles RHP Ubaldo Jimenez, on the disabled list with a sprained right ankle, threw a 44-pitch simulated game Friday afternoon. "If he feels well (Saturday) we have a schedule for him to go out and pitch once, maybe twice" manager Buck Showalter said. "He's going to have to get some innings." . Baltimore 3B Manny Machado missed his fourth straight game with a sore back but is close to returning. Showalter said Machado was available Friday and expects to start him this weekend. . With the addition of Morales, the Mariners sent DH Jesus Montero back to Triple-A Tacoma. Montero was with the big club for just one game. . Hernandez surpassed 1,000 innings at Safeco Field. Among active pitchers, only Mark Buehrle (now with Toronto) has more innings pitched at one venue - 1,306 2-3 at U.S. Cellular Field.