The Boston Celtics made their strongest case yet that they belong in that conversation on Monday, thumping the Toronto Raptors 111-89 with a wire-to-wire Game 5 blowout in their second-round series. With stingy defense, balanced scoring and an eerie steadiness, Boston took a 3–2 series lead and left the defending champs frazzled, bickering and searching for solutions with motivational button-pushing.

There is one obvious missing piece from Boston’s title dreams: proof of concept. Unlike LeBron James’s Los Angeles Lakers and Kawhi Leonard’s Los Angeles Clippers, the Celtics lack a signature superstar who has been there before. But their case as a leading contender, which grew stronger over the second half of the regular season, has only been bolstered by exceptional play in the NBA’s bubble.

Since arriving at Disney World in July, the Celtics have posted a 12-5 record, including a commanding first-round sweep of the Philadelphia 76ers. During the playoffs, they rank first in net rating and first in defensive efficiency thanks to a well-fitting starting lineup built around backcourt stopper Marcus Smart, versatile wings Jayson Tatum and Jaylen Brown, and mobile big man Daniel Theis. That group helped Boston race to an 18-5 lead in Game 5, blitzing a Toronto lineup that featured five players from last year’s title team.

In the series’ swing game, Boston was more focused, energetic and explosive despite Toronto’s growing momentum entering Monday. After Boston claimed a 2-0 lead, OG Anunoby’s Game 3 buzzer-beater threatened to turn the series upside down and Kyle Lowry’s masterful Game 4 performance evened things up. If Boston’s relative inexperience was going to show, this was the moment. Those fears proved unfounded.

“It’s about the process of growth and showing that resilience,” Celtics Coach Brad Stevens said after Game 5. “You can’t go through a playoffs without having heartbreakers. You can’t go through a playoffs without something bad happening. You just have to be able to respond. I knew we had good competitive character. You really saw that on display.”

Boston never let Toronto make a real run, a fact that clearly frustrated Lowry late in the third quarter. As he appealed to the referees for friendlier treatment, he was whistled for a technical foul with the Raptors trailing by 24 points. Serge Ibaka made it clear he had heard enough from his teammate.

“Come on, we’re losing, man!” Ibaka shouted within earshot of courtside media members as he gestured toward the scoreboard. Fred VanVleet came over to help Ibaka cool off, while Lowry relented and said, “OK, I’m done.”

The Celtics’ lack of mistakes had to be maddening for a proud Raptors team desperately seeking a comeback. Their defensive rotations were crisp, their second-unit players continued to provide quality contributions and their entire starting five finished in double figures, with nary a complaint about shots or touches.

Brown led the way with 27 points and Kemba Walker added 21. Stevens also enjoyed a scoring punch from backup guard Brad Wanamaker, but fellow subs Robert Williams, Semi Ojeleye and Grant Williams have all helped cover for Gordon Hayward, who has been sidelined by an ankle injury since the first round.

While the three top favorites entering the bubble – the Milwaukee Bucks, Lakers and Clippers – have struggled with their chemistry and cohesion to varying degrees, the Celtics have presented as a unified group.

That’s especially true on the defensive end, where bubble teams have had to grapple with high-scoring and hot-shooting offenses. Brown has held Raptors all-star forward Pascal Siakam in check, and the unheralded Theis has proven strong enough to make Philadelphia center Joel Embiid work for his points and versatile enough to track Ibaka and Marc Gasol on the perimeter.

Raptors Coach Nick Nurse raved at length about Boston’s defense on Monday, praising, in turn, their commitment in transition, their physicality, Theis’s activity, the length of their wings and their discipline. The newly minted Coach of the Year then jabbed at Siakam, who was held to just 10 points in Game 5, in hopes of inspiring a much–needed breakthrough in Game 6 on Wednesday.

“I’m not sure why he’s been so out of rhythm since the restart in the bubble,” Nurse said. “He hasn’t had a lot of great games. It’s too bad because he was spectacular in last year’s playoffs and spectacular all year long. We still have some games to play. Hopefully, he can get his rhythm.”

If Boston can put away Toronto, it would probably enter an unexpected Eastern Conference finals showdown against the Miami Heat, who are up 3-1 on the Bucks. The Heat (7-1 in the playoffs) share many characteristics with the Celtics: they have played well on both sides of the ball, they rely on communal scoring rather than a superstar headliner, and their best players, Jimmy Butler and Bam Adebayo, still have a lot to prove in the postseason.

More than anything, Boston and Miami are united by their readiness to shake up the title picture. Butler was disgusted when a possible sweep slipped away in an overtime loss on Sunday, admitting that the Heat “relaxed a little bit (and) stopped playing basketball the right way” when Bucks star Giannis Antetokounmpo went down with an ankle injury.

Tatum, a 22-year-old superstar in the making, took a similar approach Monday, choosing to focus on the lessons from Boston’s narrow losses to Toronto – like avoiding complacency and finishing off wins – rather than its decisive Game 5 performance.

“It’s a good feeling when you game plan and talk about something and go out and do it,” he said. “It’s also frustrating. If we can do it, why don’t we do it every time? Some of it is human nature. Us as professionals, we have to take more responsibility. It’s the playoffs, it’s going to be tough.”