Game 2 will not wait for the Celtics to get healthy, and neither will the Heat

Boston Celtics coach Ime Udoka took some solace in his team winning three of the four quarters in a 118-107 loss to the Miami Heat in Game 1 of the Eastern Conference finals, but he has a mountain to climb managing a roster that is missing two starters and playing a hobbled third entering Thursday's Game 2.

The Celtics left their second-round series against the defending champion Milwaukee Bucks as favorites to reach the NBA Finals, but news broke shortly after Sunday's Game 7 win that Defensive Player of the Year Marcus Smart exited Boston's arena in a walking boot. Udoka revealed on Monday that Smart suffered a right mid-foot sprain before being removed with two minutes left in a blowout and his status was in doubt.

When the Celtics' injury report dropped in the hours before Game 1, Smart was ruled out, and in another stunning blow to their top-rated defense, Al Horford entered health and safety protocols for COVID-19.

The Celtics still stifled the Heat's offense for much of the first half on Tuesday, when Jayson Tatum scored 21 of his 29 points to give them a 62-54 lead at the break, but they felt the absence of their two defensive leaders on Miami's 22-2 run in the opening six minutes of the third quarter. That was all the Heat needed.

"Obviously, Al and Marcus are veteran guys who calm us down at times," Udoka said after the loss. "You might miss that some, but it was a little bit of everybody. It wasn't just young guys and Payton [Pritchard] and those guys. It was Jayson and some of our veterans making the same mistakes, so no excuse there."

Miami felt no sympathy for Boston, since six-time All-Star point guard Kyle Lowry is also sidelined with a left hamstring injury, and the Heat have hardly needed him, winning all seven of his missed playoff games. Milwaukee will not shed a tear, either, after losing to the Celtics without three-time All-Star Khris Middleton.

The Celtics hardly had time to process their injuries in the single off day between physical series against the Bucks and Heat. Playing without Smart and Horford increased the difficulty level for an already tired team.

"We've got to be even more disciplined," said Jaylen Brown. "Obviously, we weren’t prepared to be without Al. We definitely weren’t prepared to be without Al and Smart. It's not an excuse; we've got to be better."

Smart is Boston's answer to Jimmy Butler's inspirational effort and held the Heat star to 23% shooting in their individual matchups during the 2020 Eastern Conference finals. Butler scored 17 of his 41 points in the game-changing third quarter and relentlessly hunted backup Celtics point guard Payton Pritchard all night.

Likewise, Horford's ability to space the floor on offense figured to limit Bam Adebayo's interior presence, but the Heat center had free rein of the paint helping off non-shooting Celtics bigs Robert Williams III and Daniel Theis. Boston could manufacture no offense in Adebayo's vicinity during Miami's 22-2 landslide.

Making matters worse, the Celtics lost Williams with six minutes left in the fourth quarter, when Adebayo's foot caught his lower left leg. Williams missed the first two games of the playoffs following a procedure to repair a tear in his left meniscus and sat the final four games against the Bucks with a bone bruise in the same knee. Williams started Game 1 against the Heat and played well in his 28 minutes, totaling 18 points (6-8 FG, 6-7 FT), nine rebounds and two blocks. He was Boston's only player with a positive plus/minus.

In a bit of welcome news for the Celtics, Udoka suggested Williams should return for Game 2.

"I think Rob just got a cramp in his calf from what I heard," he said, "so nothing to do with his knee."

Udoka asked 20 minutes of Theis, the third-string center behind Tatum and Williams. Smart's absence necessitated 30 minutes from Pritchard, who attempted more shots than he had in all but one game in his career, and 11 minutes from Aaron Nesmith, who played seven garbage minutes in the first two rounds.

Miami has proven it can win starting Gabe Vincent in place of Lowry at point guard. Vincent averaged 23 minutes throughout the regular season and started 27 games. He scored 17 points on 10 shots in Game 1.

"Doesn't matter who is on the floor," Vincent said of the injuries for both teams.

Boston's health is the bigger concern now. The Celtics did not rule out Horford for Game 2, but without negative PCR tests over the next two days, the earliest he could return is Game 3 on Saturday in Boston. Likewise, Smart's right foot was still sore and swollen with "limited basketball movements" on Tuesday.

"We'll see how he feels tomorrow after some more treatment and time off," said Udoka.

Just one of those guys back in the lineup would significantly increase Udoka's rotational flexibility. Without either, he can try stealing some of Theis' minutes with Grant Williams as a small-ball center, but that means more dependence on Pritchard and Nesmith. Any offense from Derrick White would help, but he, Tatum and Brown have only played a handful of meaningful possessions with Grant Williams as their center all season.

The relentless Heat are hard enough to handle at full strength. Facing them on one day of rest when they have had four is all the more difficult. Doing so without Horford and Smart was too much ask in Game 1. Both are expected back in the series, but Miami is not going to help Boston off the mat in the meantime.

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Ben Rohrbach is a staff writer for Yahoo Sports. Have a tip? Email him at rohrbach_ben@yahoo.com or follow him on Twitter! Follow @brohrbach