PHOENIX — Gunnar Henderson returned last week against the Kansas City Royals, but Henderson really returned Monday night at Chase Field. Twice, when he turned on pitches and rifled them to right field with exit velocities eclipsing 100 mph, Henderson looked himself.

He really looked like himself when he twice took off and stole second base, with his head-first slides proving his intercostal muscle strain is long behind him. That, maybe, gave the strongest indication that Henderson was back.

No, no.

Perhaps it was the bat toss that most epitomized Henderson’s return — the emphatic fling toward his own dugout upon ball four, followed by the flips of his elbow guard and shin guard.

Take it as one, any and all, and it was Gunnar being Gunnar.

“Gunnar being Gunnar is a really good thing for the O’s,” right fielder Ryan O’Hearn said.

The performance from Henderson during Monday’s series-opening win against the Arizona Diamondbacks is a strong sign that Henderson is poised to return to his game-changing ways immediately.

Before the game, manager Brandon Hyde acknowledged that Henderson hadn’t looked himself in Kansas City. He struck out in seven of his 13 plate appearances with one hit. The lack of a full spring training because of a rib injury was evident in the lack of timing at the plate.

But Hyde noted that when Henderson did get going, “it’s going to come quick.”

And it came quickly Monday, when Henderson rocketed a 106.3-mph double to right field in the third inning and followed it with a 102.5-mph single in the fifth. Henderson also walked in the sixth, and he flung his bat in characteristic form before notching his fifth career two-steal game.

“This looked like he’s getting his timing back,” Hyde said afterward, and Henderson agreed.

“The injury was never bugging me,” Henderson said of his rehab outings or his first four major league games of the season. “It was just a matter of getting the timing down and just getting my feet up under me.”

Henderson is a spark plug of sorts for Baltimore. He won the American League Rookie of the Year award in 2023 and followed it with MVP votes last season after he finished with a .281 average and an .893 on-base-plus-slugging percentage.

Henderson suffered the strained rib muscle while leaping for a ball at shortstop Feb. 27, and he missed the rest of spring training. He returned to play five Triple-A Norfolk games in a bid to make up for the absence of a ramp-up month. The 23-year-old promptly lofted two homers as part of his five hits.

“Felt like timing was pretty good but obviously don’t get the major league reps until you’re actually here,” Henderson said. “Stunk that I missed that much spring, but glad to be back now.”

With the way he played Monday, Henderson is well and truly back now. The Orioles missed that over the first two series. They missed it during the third series as Henderson rediscovered his form.

Now, the Orioles could reap the benefits of an electric player who looks like himself once more.

“That’s Gunnar, right?” O’Hearn said. “I feel like he sets the tone for us. The way he takes the extra base, stealing second all the time. And just, you know, how hard he plays. It kind of gets everybody else going and in that mind frame.”