CINCINNATI — The last time he set foot in Great American Ball Park? Brett Gardner didn’t have to think too long about that one.

“All-Star Game two years ago,” the Yankees’ veteran outfielder answered correctly on Monday afternoon. “Obviously some good memories here. Good to have my kids on the field for the Home Run Derby, stuff like that. Stuff that I’ll definitely cherish forever, never forget. That was a special time for sure.”

A funny thing happened in between visits to the home of fictional radio station WKRP, however: Gardner didn’t perform like an All-Star for the bulk of that period. Only now, upon his return, does he carry that special vibe again.

The Yankees’ leadoff hitter contributed an insurance two-run homer Monday night to help his club post a 10-4 victory over the Reds. With the game’s best record (21-9) and a six-game winning streak, the Yankees are living so large that they easily shook off what could have been a baseball-induced hangover after requiring 18 innings to outlast the Cubs Sunday night into Monday morning at a chilly Wrigley Field. Ace Masahiro Tanaka, who flew ahead Sunday and therefore avoided the Windy City madness, gave the Yankees the length they needed with seven innings and 112 pitches.

The next-to-last batter Tanaka faced, Reds icon Joey Votto, ripped a two-run homer to cut the Yankees’ lead to 7-4. So this game could have turned the wrong way, considering the Reds began the day atop the National League Central and ranked second in the league in runs scored.

Then pinch-hitter Starlin Castro led off the eighth inning with a single, and Gardner followed with a blast deep into the right-field stands, his sixth of the season — all coming the last nine games, during which time he has hit .375/.432/.875. Consider that Gardner, who owns an 11-game hitting streak overall, went deep seven times in 547 at-bats last season.

“He has power,” Joe Girardi said of Gardner. “We have seen him do it. He is not missing pitches right now. He has had a really good month of May and has had some big hits for us.”

“[I’m] being a little more aggressive, but just staying down on my legs and being more consistent at the plate. My timing’s been a lot better,” Gardner said after the game. “It helps when you’re in the lineup with a bunch of other guys that are swinging the bats so well. They don’t want to walk a guy like me to get to them, so I get good pitches to hit.”

Whatever the cause, Gardner, with an overall slash line of .260/.358/.481, hasn’t raked like this in a while. He hit .302/.377/.484 in the first half of 2015 to get that All-Star Game berth (as an injury replacement) and then plummeted to .206/.300/.292 after the break. Last year, he produced a .261/.351/.362 line, getting on base sufficiently while putting up his lowest home run total in a full season since he went deep only five times in 2010 (he played in only 16 games in 2012).

When he went .188/.316/.234 in his first 18 games of 2017, folks fairly speculated whether he would play his way to the bench in light of Aaron Hicks’ explosion and Jacoby Ellsbury’s bounce upward. Girardi pointed out on Monday that Gardner bruised his jaw and strained his neck in an April 12 collision with Rays first baseman Rickie Weeks; he went .118/.286/.147 in his first 11 games after that.

“You often wonder if that collision affected him,” Girardi said. “You want to say no, but sometimes soreness in some spots may cause you to swing a little bit different and it just messes you up.”

“It affected me in some ways, I’m sure, but I’m not sure how much,” Gardner said. “If that hadn’t happened, I may have struggled even more so for the next few weeks. You never can tell. I’m not one to try and pinpoint things.

“I’m feeling good. That’s the main thing.”

He’s looking really good. Like an All-Star once more.