Paul Blackburn’s “unusual” season saw yet another odd episode late on Tuesday night. He was startled awake by a hotel room door knock from a messenger after not hearing a phone call telling him about the Mets’ plans to activate him from the injured list the following day.

At that point Blackburn was set for a rehab start for Triple-A Syracuse.

The Mets had used Justin Hagenman for four innings of relief during their win against the Braves and needed Blackburn to take Hagenman’s spot in the bullpen.

“Definitely surprised,” Blackburn said Wednesday at Citi Field before the Mets lost 11-6 to the Braves.

Blackburn was utilized on this night, pitching the final five innings and allowing two earned runs.

“He saved the bullpen,” manager Carlos Mendoza said.

Even so, whether the veteran Blackburn will stick for long is unclear.

The Mets will need a roster spot to call up Nolan McLean for his major league debut on Saturday.

Blackburn, who doesn’t have a minor league option remaining, is a prime DFA candidate.

Blackburn, who spent six weeks on the IL with a right shoulder impingement, had last pitched for the Mets on June 28 in Pittsburgh.

It’s a season in which he also missed two months rehabbing from knee inflammation.

Blackburn also had a stomach virus that contributed to resetting his rehab clock early in the season.

Overall, he’s pitched in 12 minor league games as part of rehab assignments this season.

There have been times he was on the brink of return only to remain on a rehab assignment — with the Mets perhaps trying to maximize the roster.

In seven appearances (four starts) for the Mets he’s pitched to a 6.85 ERA.

“I just want to be in a place and pitch, really,” Blackburn said. “I just want to be somewhere and pitch.”

Meanwhile, the Mets had to delay a ceremony planned before the game that was meant to celebrate Pete Alonso for surpassing Darryl Strawberry as the franchise’s all-time home run leader because of heavy rain.

Alonso hit career homer No. 253 on Tuesday to break the record before adding No. 254.

The ceremony is now scheduled for pregame on Thursday.

The Mets set a franchise record for a season on Tuesday with a third game in which they hit at least six home runs.

The season high was seven in Philadelphia on June 21.

Entering the day the Mets were the only MLB team this season with three games in which they hit at least six homers.

All of Tuesday’s six homers occurred with two outs — only the fifth time that has occurred in MLB in the expansion era (post-1961).