The Red Sox returned to Fenway Park riding a wave of momentum. Having just taken two out of three from the Houston Astros, the club had survived one of its toughest road trips of the season and looked set to keep pushing back into playoff position.

But waiting on their doorstep was one of the hottest teams in baseball, and the Arizona Diamondbacks had no interest in laying out the welcome mat.

The Diamondbacks routed the Red Sox 12-2 in Friday’s series opener, stacking up five runs on starter Brayan Bello before Eugenio Suarez finished things with a grand slam off Josh Winckowski in the seventh.

The loss ensures Boston will remain at least 3.5 games below the playoff cutline heading into the weekend.

For Bello, Friday was a step backwards.

Coming off back-to-back outings in which he allowed one run over six innings, Bello found himself in trouble right out of the gate. He allowed two first-pitch singles and a walk to load the bases with no outs in the first, and then he walked Josh Bell to drive in a run before giving up a sacrifice fly to Lourdes Gurriel Jr. to make it 2-0.

The Red Sox answered right back with a run in the bottom of the first on back-to-back doubles by Jarren Duran and Wilyer Abreu, and after that Bello settled down and got into a groove. He held the Diamondbacks scoreless through the next four innings and never allowed any runners to get any further than first base, but things came unglued in the sixth as he ran into trouble again.

Bello got a leadoff groundout before allowing the next four batters to reach safely. He walked Gurriel, gave up an infield chopper to Adrian Del Castillo and hurt his own cause by flinging the ball wildly past first on a play he had no chance of making. That put runners at the corners and Suarez capitalized with an RBI single to extend the Arizona lead.

Then Luis Guillorme delivered the dagger with an RBI double to make it 5-1, and Bello’s day was done.

Bello allowed five runs on seven hits and four walks over 5.1 innings, and Friday marked his fourth straight start with at least three walks, and also his ninth in 24 starts.

The Red Sox offense couldn’t mount much resistance against Diamondbacks starter Ryne Nelson, who retired eight straight batters after the two early doubles and kept Boston off the board until Rob Refsnyder hit a towering solo home run to right field in the bottom of the sixth.

That made it 5-2, but the game didn’t stay close for long. Joely Rodriguez, who’d just been called up from Triple-A and cleaned up Bello’s mess in the sixth, hit Joc Pederson with a pitch to lead off the seventh and gave way to Winckowski. The Diamondbacks proceeded to load the bases and with one out Suarez took a 1-0 cutter to the Green Monster seats for a grand slam.

Arizona scored three times more off Winckowski in the ninth on a Geraldo Perdomo RBI double, a Corbin Carroll sacrifice fly and a Jake McCarthy RBI groundout. Winckowski allowed six runs on eight hits and a walk over his three innings, during which he threw 55 pitches.

Suarez finished 2 for 5 with 5 RBI and Josh Bell went 3 for 4 with an RBI. Boston was led at the plate by Refsnyder, who went 1 for 3 with the home run after subbing in when Tyler O’Neill was scratched late due to left fourth finger inflammation, and Ceddanne Rafaela made a handful of strong defensive plays at shortstop, including one full-extension diving catch on a shallow fly ball in left field.

The Red Sox (67-60) will look to bounce back against the Diamondbacks (73-56) on Saturday, when Kutter Crawford (8-10, 4.25) takes on Arizona’s Zac Gallen (9-6, 3.85).