The frenzied final 48 hours before Thursday’s 3 p.m. ET NBA trade deadline posed a challenge for the Celtics as they arrived in Dallas to face Cooper Flagg and the Mavericks.

Hours before tip-off, the Celtics reportedly traded guard Anfernee Simons to the Bulls for center Nikola Vučević. Simons was immediately downgraded from available to out due to personal reasons, stripping Boston of its leading bench scorer and leaving a void in the rotation. Luka Garza, finding confidence beyond the arc in Dallas, filled that void.

Garza played 20 minutes off the bench in Boston’s 110-100 win on Tuesday night, and carved out his domain at the top of the key, rewarding feeds from Payton Pritchard.

“That’s generally where you get most of your shots off the pick-and-pop. It’s always an above-the-break kind of area, so I try to work on that a lot,” Garza told reporters, per CLNS Media. “Over time, I’ve grown more and more confident in it, and my teammates trust me. If I get it and get into a good rhythm stepping into the ball, I feel like I’m knocking it down.”

Three times, Garza used the pick-and-pop to create space at the top of the key, and three times he knocked down a 3-pointer from that spot. He finished with 16 points on a perfect 4-for-4 shooting from deep, tying his career high for made threes in a game. It marked Garza’s most in-sync performance from beyond the arc in a Celtics uniform, as he grew into a critical part of the offense throughout the night.

“Anytime you can catch a rhythm and make some shots in a stretch like that where our offense is really going, it’s definitely big time,” Garza told reporters. “So I know they’re important, especially when we’re playing guys like Gafford who are sitting in a drop. One way you can expose that is by stretching the floor and giving guys more space. That’s what I’m trying to do.”

Garza’s four made 3-pointers tied his second-most attempts in a game this season and marked the fifth time in his career he has hit at least three.

Boston’s ability to lean on Garza as a floor spacer — a role he rarely occupies — helped offset the loss of Simons in a way opposing defenses wouldn’t typically anticipate. Garza is shooting a career-best 47.6 percent from three on limited volume (1.5 attempts per game), well above his career average of 36.1 percent. Typically, his greatest impact comes on the offensive glass, where he turns teammates’ misses into second-chance opportunities and forces opponents to pay for defensive miscues.

In Dallas, Garza showcased one of the most important aspects of his growth: his versatility.

“Luka is able to give us advantages in different ways,” Celtics head coach Joe Mazzulla told reporters, per CLNS Media. “Sometimes he’ll force a veer and get us an offensive rebound. Sometimes he’ll just get us open threes. Today, it was his ability to pop and force 2-on-1s that way. I thought we missed him on a couple in the first half, then our guys made an adjustment and got him open looks in the second half, which forced them into different defensive coverages and allowed us to execute in different ways.”

As the Mavericks focused on guarding Boston’s usual offensive threats, such as Jaylen Brown, Derrick White, and Pritchard, Garza capitalized on the openings he found. He recognized that Dallas wasn’t accounting for him as a perimeter threat, and he turned it to his advantage, proving he could knock down multiple three-pointers and become a legitimate weapon from that spot on the floor.

Garza’s efforts to build confidence as a shooter didn’t come at the expense of his usual duties as a backup frontcourt player. He still grabbed four rebounds (all offensive), added two steals, an assist, and a block, proving he can be a Swiss Army knife in limited minutes off the bench.

“I thought Luka was great in the second half,” Mazzulla added.

With Simons out of the equation, Mazzulla was forced to make adjustments. He removed Pritchard from the starting lineup for the first time this season, slotting him into the sixth-man role, and moved Baylor Scheierman into the starting five. It was a change, but not one the Celtics weren’t prepared for, as they had spent the season stressing the importance of their core principles and delivering a clean, on-brand 48 minutes of basketball.

This approach allowed Boston to withstand Flagg’s 36 points while also creating an opportunity for Garza to take a step forward in his development.

“This year, our margin for error has been slim,” Brown told reporters, per CLNS Media. “If we don’t come to play, if the other team wins the margins, we’ll lose games that we’re supposed to win. Those film sessions we’ve had — I call them Celtics University — it’s like a classroom. Everybody’s got their notepads, asking questions, breaking down the film and the details of everything, because the details are most important. The difference between good and great players is the details.”