In the early innings of Sunday’s series finale the Red Sox looked like a team on the cusp of finally turning their frigid start to the season around.

Boston took a 4-0 lead and knocked San Diego Padres starter Walker Buehler out of the game in the bottom of the third.

Then Ranger Suárez came undone, Greg Weissert found himself on the receiving end of a Manny Machado go-ahead blast and the Red Sox dropped their home opener series 8-6.

A start that began oddly but meticulously for Suárez ended prematurely and in concerning fashion. After facing the minimum number of Padres batters through three innings, the Red Sox starter exited one batter into the top of the fifth, charged with four earned runs on six hits, two walks and two strikeouts.

The Padres were unable to keep runners on the bases early on, thanks in part to Suárez, who flashed Gold Glove-caliber defense in the first three innings. The Red Sox starter issued a one-out walk to right fielder Fernando Tatis Jr. in the top of the first, and then started an inning-ending 1-6-3 double play on a comebacker from centerfielder Jackson Merrill.

In the top of the second, Miguel Andujar reached base on a throwing error by veteran shortstop Trevor Story, only to be out advancing to second on a quick recovery and throw by first baseman Willson Contreras. Former Red Sox shortstop Xander Bogaerts singled to right with two outs in the inning, only to be gunned down at second by Wilyer Abreu, who’s coming off back-to-back Gold Glove seasons and whose cannon arm rarely misses the mark.

Suárez recorded the first two outs of the third, a 1-3 putout and an unassisted out at first base. But in the fourth, the Padres rose up en masse. Eight men came to bat and tallied three runs on four hits, a walk and a second Red Sox error. Suárez, who needed 42 pitches (and an automatic strike) to get through the first three innings, threw 32 alone in the fourth.

The rally began with a Tatis 105.3 mph one-out double to center. Merrill followed with an RBI single to put the Padres on the board, and Machado singled to put runners on first and second. The pair advanced to second and third when catcher Carlos Narváez attempted to pick Machado off at first, and the ball caromed off the Padres third baseman’s foot and away from Contreras.

Suárez struck out Andujar, but walked Bogaerts to load the bases. Nick Castellanos’ two-run single to left made it a one-run game before Suárez got Jake Cronenworth to line out to strand two.

“They made an adjustment,” Cora said of the fourth inning. “He’s a groundball pitcher, so we’re ahead in the count, we got a groundball, we probably get out of the inning. But we didn’t help ourselves. I think in that inning they became very aggressive, but we made some decisions there that put them in a good spot to score runs.”

After Tatis’ double, each Padres hit in the fourth came on the first pitch. So too was Luis Campusano’s leadoff single in the fifth, which brought Cora out to collect his starter.

For the second time in five appearances this season, Weissert turned a lead into a deficit. After recording two strikeouts in the fifth, the righty reliever gave up a first-pitch single to Merrill and a three-run homer to Machado, who was booed vociferously as he rounded the bases (and throughout the weekend).

Deflated, the Boston bats went 1-2-3 in the bottom of the fourth and fifth. Facing reliever Bradgley Rodriguez in the sixth, Masataka Yoshida and Narváez singled and stood on the corners as Roman Anthony struck out swinging on three pitches to end the inning.

The Red Sox were seven outs away from becoming the second team in franchise history to fail to score six or more runs in any of their first nine games of the season (1964) when Abreu and Yoshida tied the game with their third hits of the day, a double and two-run double, respectively.

The tie game vanished in the blink of an eye in the top of the eighth. Tyler Uberstine, back on the mound for the third inning of his MLB debut, threw a 2-2 four-seam fastball to Merrill, who sent the pitch soaring into the seats atop the Green Monster for a leadoff home run.

In response the Red Sox returned to the dugout and went down in order in the bottom of the eighth.

Facing righty Zack Kelly, San Diego tacked on an insurance run in the ninth on a leadoff pinch-hit double by Gavin Sheets and a sac-fly by Tatis.

As the game neared the three-hour mark, flame-throwing Padres closer Mason Miller blazed through the bottom of the ninth. He struck out Story (on three pitches), Jarren Duran and Contreras to complete San Diego’s comeback.

The Red Sox tallied nine hits, four walks and struck out 10 times. They were 5 for 11 with runners in scoring position and left seven men on base.

Story entered the day tied with teammate Ceddanne Rafaela, who didn’t start Sunday’s game, for third-worst chase rate in the majors (51.2%), and went 1 for 5 with two strikeouts in the contest. He’s now batting .119 with a .333 OPS, and has made three errors.

Asked if he still wants Story hitting in the No. 2 spot in the lineup, Cora answered, “I still like Trevor Story as a player.”

The Red Sox are 2-7 to start the season for just the sixth time since 1950. They open up their fourth series Monday evening, against the incoming Milwaukee Brewers, who are 7-2.