MEMPHIS — The Celtics had lost their last two games against teams with losing records, and at the start of the fourth quarter against the Grizzlies on Saturday, they faced the very real prospect of it happening once more.

The Celtics had let a 19-point first-half lead evaporate, and in the third quarter Marc Gasol almost singlehandedly demolished them with 21 points, staking his team to a 2-point lead.

But this time, Boston woke up from its slumber before it was too late, starting the fourth quarter with a massive 16-o surge that Memphis had no real answer for, and the Celtics grabbed a 102-93 win.

Kyrie Irving led a balanced Celtics attack with 20 points. Jayson Tatum, who was coming off his worst shooting night of the season, bounced back with a 19-point, nine-rebound effort.

Celtics coach Brad Stevens questioned his team’s effort in its home loss to the Jazz on Friday. And in the first quarter here Saturday, it appeared the message had been received.

On offense, the Celtics were crisp and calculated, and on defense they turned every Memphis possession into a chore, as the shot clock gave the Grizzlies as many problems as Boston did.

The Celtics had a 10-0 run that was followed soon after by a 9-0 burst. They took a 31-12 lead after holding Memphis to 4 of 18 shooting with five first-quarter turnovers.

Before the game Grizzlies interim coach J.B. Bickerstaff said that to find holes in Boston’s top-ranked defense, his team would have to accelerate the pace and look for opportunities in transition. That is what Memphis started to do in the second quarter, thanks in part to the Celtics’ miscues.

The Grizzlies’ 15-5 run to start the second quarter included a pair of fast-break dunks and some hot shooting by Tyreke Evans, who made all three of his 3-pointers and had 15 points in the period.

Memphis trailed, 48-40, at halftime and continued to attack in the third behind Gasol (30 points), who scored 10 straight Memphis points early in the period.

With the score tied at 60, the Celtics had a 9-0 burst, but once again Gasol had an answer. The big man scored 11 more points in the final 3:09 of the third quarter, including three 3-pointers from the left arc.

Stevens grew increasingly exasperated after each one, pleading with his players to stop him or slow him or do something to make his night more difficult. Gasol’s last 3-pointer of the surge, with eight seconds left, gave Memphis the 73-71 lead it took to the fourth.

But the Grizzlies’ hopes would be dashed soon after. Al Horford made consecutive baskets and then fed Terry Rozier for two more. Then Tatum threw down a fast-break dunk before adding a 3-pointer, and the Grizzlies were dazed. Daniel Theis, playing with a mask covering his broken nose, finished off the game-defining 16-0 burst with a 3-pointer.

Memphis, which was held scoreless for 5:33 during that run, made one last push, as a Mario Chalmers 3 pulled it within 97-91. But that was as close as the home team would get.

.   .   .

Theis was cleared to play despite breaking his nose during the first half of Boston’s loss on Friday night.

The Celtics initially said Friday that Theis would not join the team for Saturday’s game, but Theis was able to undergo an X-ray at a Boston hospital and make it to the airport in time for the team’s flight.

He wore a mask in Saturday’s game, although it was not custom-fitted. He will have one made soon, and he said he expects to wear it for several weeks. Stevens also said that Theis will have to have the nose “reset’’ soon, and that he likely will be sidelined for a day or two when that happens.

Theis suffered the injury when he was elbowed in the face by Utah forward Ekpe Udoh in the first quarter on Friday. Blood gushed from his nose and he did not return to the game.

“I just didn’t expect so much blood,’’ Theis said. “When I got hit, I felt like, ‘OK, I got hit.’ But not like I’m going to break my nose. It was like water. I just ran back. I didn’t want the ball.’’

Theis, who entered Saturday averaging 4.3 points and 3.8 rebounds per game this season, said he has had no trouble breathing. Irving suffered a facial fracture in the Celtics’ Nov. 10 win over the Hornets and wore a protective mask for one month.

“I can’t keep track of all our facial gear right now,’’ Stevens said. “But we’re just glad [Theis] is OK.’’

.   .   .

Last summer, Stevens invited then-Grizzlies coach David Fizdale to Boston to meet with his staff.

“We were picking his brain on all the different things he does,’’ Stevens said, “because I thought he was one of the best.’’

Fizdale, a longtime NBA assistant, led the Grizzlies to a 43-39 record and a Western Conference playoff berth during his rookie season as a head coach last year. This year, Fizdale was fired after the Grizzlies got off to a 7-12 start that included an eight-game losing streak. Still, the move stunned many people around the NBA, particularly considering the Grizzlies’ injury issues.

“I thought the job that Fiz did last year here and at the start of this year — any of us can go on an eight-game losing streak any time. I mean, this league is tough,’’ Stevens said.

“It’s all about kind of the long haul. I think he’s one of the brightest, most fun coaches that I’ve seen.’’

Stevens said he is sure Fizdale will get another opportunity as an NBA head coach.

.   .   .

Bickerstaff was named the Grizzlies’ interim head coach after Fizdale’s firing. Bickerstaff said he has been impressed by the Celtics’ growth under Stevens.

“One of the things when you look at a coach is, how often does his team reach its potential or exceed their potential?’’ Bickerstaff said. “And I think throughout his tenure in Boston, they’ve done that. So you’ve got to give them credit.’’

Bickerstaff added that the Celtics’ front office has done a good job assembling this roster with long, versatile wings.

“They put in some skilled guys, but guys who come with a natural toughness and basketball IQ and versatility,’’ he said. “You look out there sometimes and they’re playing five guys that are 6-7 and under, but they’re all skilled. They can beat you from inside and out and they all want to defend you one-on-one.’’