PHILADELPHIA -- When the Philadelphia 76ers were going through their historically horrendous 1972-73 season, they were the team opponents wanted to play to get better.

The 2015-16 team, which also has produced just nine wins, gave Boston a bit of a challenge at times Sunday, but the Celtics left the Wells Fargo Center feeling a little better about themselves.

Having entered the game losers of four of six and having dropped from third to sixth in the Eastern Conference playoff standings, the Celtics recorded a desperately needed 120-105 win over the woeful Sixers.

"There's no question the plane ride feels a whole better when you win," Celtics coach Brad Stevens said. "We played a rough patch there, a rough stretch -- and we've got a tough one (Monday at Indiana) -- but you've got to do what you can to focus on the now."

Led by the overpowering Amir Johnson (18 points, eight rebounds), a solid floor game from Evan Turner (17 points, nine rebounds, six assists) and timely baskets from Isaiah Thomas (26 points, 10-for-10 from the line, eight assists, six rebounds), the Celtics held off a hungry and energetic Sixers squad that just doesn't have the talent to play with the big boys -- literally.

Johnson was a beast underneath, hitting nine of 10 shots, and Jared Sullinger bulled his way to 17 hard-fought points and 13 rebounds.

With the Sixers playing without bigs Jahlil Okafor (torn right meniscus) and Richaun Holmes (right Achilles soreness), coach Brett Brown knew his young and undermanned team was in trouble in the paint. And it was obvious from the opening tap.

In the first quarter alone, Boston (40-30) outscored the Sixers 20-4 in the paint and owned the backboards, 19-12.

Providing an efficient yet quiet 39-minute run was Boston guard Avery Bradley. He connected on seven of 12 shots, including three of four from 3-point range, to finish with 20 points.

The Sixers (9-61) tried to make it a game in the third quarter, and Stevens wasn't surprised.

"They play really, really hard," he said. "It's hard (for them to win, but) they're hungry and athletic, and we're not feeling too good about ourselves, so there were reasons to expect this to be a really tough game. Every game in the NBA is."

The Sixers, who trailed by 15 points in the second quarter, began to make a third-quarter push, getting within 76-70 before Thomas pushed back. The diminutive All-Star guard, who averaged 25.7 points a game against the Sixers in the previous three meetings, had just eight points at the half on 2-for-9 shooting. In the third quarter, Thomas knocked down 13 points, including a 3-pointer at the buzzer, giving Boston an 88-79 lead.

Setting an example for his younger teammates, 32-year-old Carl Landry kept the Sixers competitive. Battling his way against the Celtics' collection of tree trunks, Landry scored 26 points, grabbed eight boards, five on the offensive end, and allowed the Sixers to stay within single digits throughout a good portion of the fourth quarter.

"Landry killed us tonight," Stevens said. "I don't think I did a very good job -- because he hasn't played in the previous three games -- in explaining to our guys about Landry in our pregame meetings."

Despite his recent inaction, Landry came ready to play. And Brown knows he can count on the nine-year veteran.

"That's why guys stay in the league as long as they do," Brown said. "There's a professional approach to how they treat their job. And we saw that tonight with Carl.

"You find a way to get him in the game, to keep him somewhere engaged, and tonight we reaped the benefit. We needed him. We needed every bit of (his) minutes."

A floater by Nerlens Noel, off a feed from Ish Smith, got the Sixers within 96-91 with 6 minutes, 50 seconds left in the fourth quarter. Then the Sixers began missing threes and free throws, the Celtics rebounded them, and all of a sudden a 17-8 run put the game away.

"They're on a different path than we are at the moment. We're on a different type of plan," Brown said, "and we respect what they have done."

As for the losing, it can take its toll on a Sixers team full of young players trying to get used to the grind that is the NBA.

"Everybody in this locker room comes to fight every day," Landry said, "no matter what it is, practice or a game, film sessions. So I don't think it's weighing on them. As a team, we just have to get better and improve."

Hollis Thompson scored 18 points for Philadelphia, and Smith had 14 points and eight assists.

NOTES: Sixers C Joel Embiid will spend the next few weeks in Qatar rehabbing his twice-injure, twice-surgically repaired right foot. According to the 76ers, the trip to Aspetar, a well-respected orthopedic and sports medicine facility in Doha, was previously scheduled. ... Philadelphia PF Jahlil Okafor will undergoing surgery Tuesday on his torn right meniscus. The small tear will be repaired in Florida. ... Sixers coach Brett Brown said he expects PF Richaun Holmes (right Achilles strain) and SF Robert Covington (concussion protocol) to suit up Wednesday when the team takes on the Nuggets in Denver. ... Sunday night's game was the start of one of 19 back-to-backs for the Celtics.