Cubs' five-homer day wins wild back-and-forth bout with Diamondbacks

File this one under “B.” For “bonkers.”

What started as a pitching duel of sorts featuring a Cy Young winner ended in a whiplash of blown leads and big flies Friday, one of the nuttiest games you’ll see.

The Cubs and Diamondbacks combined for 21 runs after the seventh-inning stretch, both teams hit grand slams, and the Cubs got a game-winning home run from their big offseason addition, one of five long balls they smacked in a 13-11 victory.

“If you’ve seen that one,” manager Craig Counsell said, “you’ve been around for a while.”

Indeed. The 21 runs in the seventh and eighth innings were the most scored in consecutive innings in a game involving the Cubs, matching an instance from 1893 — more than 20 years before the Cubs started playing at Wrigley Field.

“It was crazy,” Counsell said. “We gave up 10 runs in an inning and won.”

That’s something the Cubs hadn’t done since 1912.

Back in the 21st century, Ian Happ’s grand slam in the seventh figured to be the necessary separation for the Cubs, who started the eighth inning up six.

But the Cubs’ bullpen collapsed in spectacular fashion, Jordan Wicks loading the bases on his first day back from the minors, Porter Hodge surrendering a grand slam and Ethan Roberts giving up a three-run homer. The Diamondbacks scored 10 in the eighth to seize the lead.

Fans went from rocking to booing but quickly got to change their tunes again when the Cubs hit three more home runs in the eighth: Carson Kelly’s second of the game, Kyle Tucker’s first-pitch laser beam that flipped the score and Seiya Suzuki’s cherry-on-top solo shot.

The lineup stayed incredibly hot, adding a baker’s dozen to its league-leading run total.

“We’re never out of a game, regardless of the score,” Tucker said. “I think today kind of showed that.”

Tucker is proving to be even better than advertised after the Cubs made their biggest offseason acquisition via the trade market rather than spend record dollars on a free agent such as Corbin Burnes, who pitched well for Arizona with six innings of two-run ball.

While Tucker was brought in to be a lineup-altering force, Kelly has perhaps been an even more celebrated newcomer, with fans loudly chanting his name on his fifth trip to the plate. Kelly had his second two-homer game of the season and matched a career high with five RBI. His OPS? A jaw-dropping 1.675.

That he has done that near the bottom of the lineup has lengthened things for the Cubs, making rallies like this one possible.

Of course, that’s a lot of production, regardless of batting-order position.

“Wherever in the order,” Happ humorously corrected. “If you have somebody just hitting a homer every time?”

And how about Colin Rea’s effort? With Justin Steele out for the season, the Cubs have a sizable hole in their rotation. Rea isn’t exactly making everyone forget about Burnes’ availability as a free agent this offseason — or canceling the front office’s search for trade-deadline reinforcements — but he has pitched well in two outings with only two runs allowed in 8„ innings.

As a blown six-run lead obviously indicates, it wasn’t all sunshine and rainbows. The pen’s implosion is another blemish on the record of the relief corps, which came in with one of the highest ERAs in the majors. It’s up to 5.83 after the 10-run eighth inning.

A day like this, even at Wrigley Field, is a rarity. But somehow, it’s something only this ballpark can deliver.

“I can’t imagine any other team is coming to their home park checking the flags on the way in, checking Lake Shore Drive on the way up, seeing if the waves are crashing or if it’s calm,” Happ said.

“We’ll see what she brings tomorrow.”