Jayson Tatum with Celtics coach Joe Mazzulla

With the Bucks—prohibitive title favorites entering the playoffs—eliminated, it looked like the Celtics would have a clear path to their second Finals appearance in as many years, holding home-court advantage over a Sixers squad they dominated throughout the regular season, winning three of their four head-to-head matchups. And while the Celtics still have a pulse (recall they trailed Milwaukee by an identical 3-2 margin in last year’s Eastern Conference semis, a series they would end up winning), the Celtics are on the precipice of a truly demoralizing loss to the Sixers, a wasted opportunity for a team that had all the right championship ingredients.

The Celtics, among other fatal flaws, have developed a frustrating habit of taking their foot off the gas, squandering late leads in Games 1 and 4, the former played without the NBA’s leading scorer and reigning MVP, Joel Embiid. Jayson Tatum’s continued slow starts aren’t helping any, while longtime Boston Globe columnist Dan Shaughnessy would argue the Celtics have carried themselves with an undeserved “arrogance,” succumbing to frequent and costly lapses. Plagued by a crippling lack of urgency, the Celtics have too often let opponents off the hook, playing with their food against a Hawks team they arguably should have swept, a trend that’s continued with a similarly undisciplined approach throughout their series with Philadelphia.

There’s plenty of blame to go around for the Celtics’ collapse, though the brunt of that criticism has fallen on rookie coach Joe Mazzulla, whose deer-in-the-headlights performance Sunday in Game 4, declining to call timeout at the end of regulation and again with a chance to win the game in overtime, has fans and media longing for the days of Ime Udoka and even Brad Stevens. Tuesday’s Game 5 brought more gripes as the Celtics struggled to dig themselves out of an early hole with Mazzulla doing little to stop the bleeding in a 115-103 Sixers rout.

“Your team was just in the NBA championship last year. How the hell does this team not come out with a sense of urgency?” Jay Williams asked Wednesday on Keyshawn, JWill and Max, going as far as to say Mazzulla has “lost the locker room.” “It feels like Joe Mazzulla is in over his head.”

Miami-based radio host and podcaster Jonathan Zaslow called out Mazzulla, both for his lack of in-game adjustments and standoffish demeanor toward the media, puffing his chest after a victory in Game 2.

“He was gift-wrapped a very good team. He has done nothing in this league,” Zaslow opined earlier this week during his appearance on The Dan Le Batard Show with Stugotz. “How about the media can ask a couple questions when you don’t use your timeouts and then, when the game is on the line, you don’t get a shot off?”

The league’s youngest coach at 34, Mazzulla replaced Udoka (now of the Rockets), who was suspended and later fired for a scandal that rocked the NBA, engaging in an improper workplace relationship with a female subordinate. For all the vitriol he’s received, Mazzulla was one of three finalists for the NBA’s Coach of the Year, leading the Celtics to their best record (57-25) since 2009. With Boston still reeling from the Bruins’ heartbreaking first-round exit on the heels of what was a record-breaking regular season, all eyes will be on Mazzulla as the Celtics head into battle Thursday night at Wells Fargo Center, needing a win to keep their dwindling title hopes alive.