SAN FRANCISCO >> A sun-kissed, sellout crowd celebrated more than just another Giants’ win Sunday at Oracle Park.

This 5-4 victory came in walk-off fashion, it secured a sweep of their home-opening series against the Seattle Mariners, and it extended baseball’s longest-active win streak to seven straight W’s.

The Giants, after sweeping their previous three-game series in Houston, own an 8-1 record, their best since the 2003 club opened 13-1.

Pinch-hitter Wilmer Flores delivered a two-out single in the ninth to score Luis Mattos, one pitch after a phenomenal catch injured Mariners’ right field Victor Robles.

Flores’ game-winner came was extra stunning considering the macabre scene it followed. Robles daringly snared Patrick Bailey flyball for the Giants’ second out; Matos tagged up and advanced from first to third on the play, but a replay review moved Matos back to second base.

Robles had to be carted off the field after his left arm collided with the waist-high wall and foul-ball netting. “He took on a wall we’ve never seen anyone take on in this park’s 25-year history,” Mike Krukow said on NBC Sports Bay Area’s broadcast. “It was one of the most spectacular catches we’ve seen in this ballpark.”

Mike Yastrzemski, whose three-run homer staked the Giants to a 4-2 lead in the fourth inning, got the game-winning rally started with a leadoff, four-pitch walk. Matos then reached on a fielder’s choice, with Yastrzemski’s slide into second base breaking up a potential double play.

Camilo Doval entered in the ninth seeking his third save of the season, and he was one strike shy of doing that. Instead, clean-up hitter Randy Arozarena lined a two-out, two-strike single over a leaping Matt Chapman at third, thus driving in Victor Robles for the tying run. Doval escaped an ensuing bases-loaded jam by getting Mitch Garver to pop out to Chapman.

Yastrzemski’s three-run homer put the Giants ahead 4-2 in the fourth inning, and it came on an opposite-field approach that had just delivered singles by Jung Hoo Lee and Heliot Ramos, the latter of whom drove in Willy Adames for the Giants’ first run of the day.

Yastrzemski’s homer, his first of the season, came on a first-pitch, belt-high fastball by Mariners starter Bryan Woo. Melvin acknowledged pregame that the Giants would emphasize urgency at the plate against Woo, an Oakland native who threw a first-pitch strike 72.9% of the time last season for MLB’s best mark since such tracking began in 1988.

Flores has reached base in all nine of the Giants’ game, but he was out of the Giants’ lineup up until the ninth inning. “I can’t run Flo out every single day. I know it’s just DH-ing and we’re getting a lot of production out of him. I want to keep him healthy,” Melvin said pregame. “This was a good day to get (Luis) Matos in there, get (Heliot) Ramos off his feet and give Flo a day off, though I still have him coming off the bench.”

After pitching six scoreless innings last week to win in his native Houston, Jordan Hicks allowed a pair of solo home runs Sunday, with Nos. 2 and 3 batters Julio Rodriguez and Cal Raleigh going deep in the first and third innings, respectively. Hicks got pulled after 90 pitches — with one out in the sixth, two men on base, and a standing ovation from a sellout crowd in his first home start of the season.

Reliever Randy Rodriguez promptly yielded an RBI single to Ryan Bliss that trimmed the Giants’ lead to 4-3. Rodriguez failed to back up Luis Matos’ throw home that bounced past catcher Patrick Bailey, and not only did that allow two Mariners to advance a base, Matos was given an error.