This season, the Celtics’ Jayson Tatum took his game up to an all-star level.

Stopping the 22-year-old, 6-foot-8 forward will be one of the major keys when the 76ers and Celtics open their best-of-seven opening-round series on Monday at the Wide World of Sports Complex in Kissimmee, Fla.

Another of the many Celtics weapons who bears close watching is point guard Kemba Walker. Walker has struggled this year against the Sixers, adapting to playing against a bigger, more physical team.

Tatum and Walker are Boston’s two leading scorers, averaging 23.4 and 20.4 points a game, respectively.

With Ben Simmons sidelined after Mondays’ surgery on his left knee, the task of guarding Tatum and how it is carried out will be among the Sixers’ biggest challenges.

Defending against Walker won’t be easy, either.

Simmons is a two-time All-Star and, according to NBA.com stats, he had 24 minutes and 23 seconds of matchup defensive minutes this year against Tatum, by far the most on the team.

“They are missing one of their best players, but they have a bunch of other guys around the same height, kind of play the same position that are interchangeable, so you know those guys are really good,” Tatum said about the Sixers on a Saturday Zoom interview.

The Sixers won the season series three games to one, and Walker played in three of the games, all losses. He shot 22-for-59 from the field (37.3%), including 11-of-30 from three (36.7%).

Josh Richardson, among the Sixers’ top defenders, will get the opening assignment on Walker.

The 6-5 Richardson has great length and can affect the 6-0 Walker.

In 11:41 of matchup defensive minutes, Walker shot 4-of-11, including 2-of-6 from beyond the arc against Richardson.

Walker has been bothered by a knee injury but he averaged 25.1 minutes in six seeding games.

“He is fine and ready to roll,” Boston coach Brad Stevens said Saturday.

Walker has great respect for Richardson, who he also faced in the 2016 playoffs when Walker’s Charlotte team met Miami.

“He’s a great defender, very active,” Walker said on Saturday about Richardson. “He has speed, he has length, he’s tall, but you know, that is where I have to rely on my teammates; they do a great job of just getting me open, giving me the opportunity.”

Boston's Kemba Walker is one of the two main scoring threats the Sixers will have to worry about.
Kyle Phillips / AP
Boston's Kemba Walker is one of the two main scoring threats the Sixers will have to worry about.

Richardson is a versatile defender and in limited time this year on Tatum, he forced him into 2-for-7 shooting (2-of-3 from three-point range).

Sixers forward-center Al Horford could also be an option to guard Tatum, his ex-Celtics teammate. In 2:38 of matchup minutes, Tatum shot 5-of-17, including 1-of-5 from three-point range.

“I haven’t seen many young guys grow as quick as he has developed his game,” said Horford of Tatum on Friday in a Zoom interview.

Sixers coach Brett Brown, whose team had off from practice Saturday, values Horford’s versatility.

“He can guard a perimeter guy, I think, better than most centers, if that’s what you want to call him, in the league.”

Sixers rookie 6-5 Matisse Thybulle is another player who could spend time on both Tatum and Walker.

Thybulle has also played his most matchup minutes against Walker (10:06). Walker shot just 4-of-12 (2-of-8 from three) against Thybulle, but made all seven foul shots. More importantly, Walker had trouble with Thybulle’s length, with four turnovers and just two assists.

In limited matchup time (3:11), Thybulle held Tatum to 2-of-6 shooting.

“He’s going to be huge as a defensive requirement, especially since you don’t have Ben, with the great wing players the Celtics have, in the upcoming series, he’s going to assume a massive role,” Brown said about Thybulle.

Brown also suggested that he’d like to get Glenn Robinson III in the mix defending the Celtics wings, which could mean some time on Tatum. Robinson, acquired from Golden State on Feb. 6, did miss six of the eight seeding games, including the last two with a left hip pointer.

Tobias Harris could be another body to throw at Tatum, although he likely will match up with Jaylen Brown.

Regardless, the Sixers will likely use several different defenders on Tatum and Walker in an attempt to wear out Boston’s two All-Stars.