Isaiah Thomas and the Boston Celtics had little trouble with a batch of Western Conference opponents — save for a hiccup in Sacramento.

Now they’re gaining fast in the East.

Thomas had 29 points and eight assists, backcourt mate Marcus Smart added 19 points against his hometown team and the Celtics beat the Dallas Mavericks 111-98 on Monday night.

Kelly Olynyk scored seven of his 15 points during a 12-2 run that started with the Celtics leading by one in the fourth quarter as the Atlantic Division leaders won for the 10th time in 11 games.

Boston pulled within two games of defending NBA champion Cleveland atop the East by finishing a 5-1 stretch against the West with three straight road wins, following what now looks like a puzzling 16-point loss in Sacramento.

“We would love to go 4-0, but things happened,” said Smart, who starred at a high school in a suburb near Dallas. “But we bounced back. That’s what good teams do. We’re becoming a very, very great team.”

Rookie Yogi Ferrell had 20 points for the Mavericks, who came in with three wins over division leaders in the past two weeks after spending the first three months at or near the bottom of the West.

Olynyk started the decisive surge with a pair of layups, followed by a high-arching layup on a drive by Thomas, the NBA’s second-leading scorer. After Olynyk hit a 3-pointer, Thomas made one for a 100-89 Boston lead.

“They’ve got a legitimate shot to get to the Finals with that team out of the East,” said Dallas coach Rick Carlisle, who played for the Celtics. “It’s a very good basketball team, so when you’re playing a team on that level, you’ve just gotta be on it from the very beginning.”

Mavericks guard Deron Williams was ejected late in the second quarter after getting two quick technical fouls for arguing a foul call, part of an 8- 0 Boston run over the final 58 seconds for the Celtics’ 61-50 lead at the break.

Williams, who was in his second game back after missing eight games with a right big toe sprain, was called for pushing off while driving for a layup. He intercepted a pass intended for official Justin VanDuyne, who made the call, and began arguing with him.

Dallas’ point guard pounded the ball on the floor with two hands while turning away as the first was technical was called, and VanDuyne quickly called the second tech.

Thomas and Smart combined for 23 points in the first quarter, but Ferrell had 13 at halftime to help Dallas get within three before Boston’s late surge.

Harrison Barnes scored 19 for Dallas, and Dirk Nowitzki and Wesley Matthews had 18 apiece.

Notes — Gerald Green played despite an illness, scoring 10 points in 13 minutes. … The Celtics swept the two-game season series after having dropped seven straight against the Mavericks. … Jae Crowder had 10 points, including a 3 to help put the game away against his former team. … Nowitzki’s 26-point average against Boston coming into the game was the highest against any opponent for the 19th-year player. … Despite the ejection, Williams got the assist he needed to pass Muggsy Bogues for 19th on the NBA’s career list. Williams now has 6,727 assists.

Next — The Celtics have back-to-back contests before the All-Star break, at home against Philadelphia on Wednesday and at Chicago on Thursday.

Celtics, 111-98

BOSTON (111)
Crowder 3-9 2-3 10, Johnson 3-4 0-0
7, Horford 5-12 0-0 11, Thomas 9-19
7-9 29, Smart 6-11 4-4 19, Green 4-8
0-0 10, Mickey 0-0 0-0 0, Jerebko 1-
2 0-0 3, Olynyk 6-10 2-2 15, Rozier
1-3 0-0 2, Young 2-3 0-0 5. Totals
40-81 15-18 111.
DALLAS (98)
Barnes 7-16 3-5 19, Nowitzki 7-17 3-
3 18, Curry 3-9 0-0 8, Williams 1-1 0-
0 2, Matthews 5-12 7-10 18, Finney-
Smith 0-0 0-0 0, Brussino 0-1 0-0 0,
Powell 0-1 0-0 0, Mejri 1-2 0-0 2,
Ferrell 8-11 2-2 20, Harris 2-6 4-5 9,
Anderson 1-1 0-0 2. Totals 35-77 19-
25 98.
Boston 30 31 22 28 — 111
Dallas 28 22 32 16 — 98
3-Point Goals_ Boston 16-34
(Thomas 4-10, Smart 3-7, Green 2-3,
Crowder 2-5, Johnson 1-1, Young 1-
1, Horford 1-2, Jerebko 1-2, Olynyk
1-3), Dallas 9-27 (Barnes 2-4, Ferrell
2-4, Curry 2-5, Harris 1-3, Matthews
1-5, Nowitzki 1-5, Brussino 0-1).
Fouled Out_ Crowder.
Rebounds_ Boston 41 (Johnson,
Olynyk 7), Dallas 37 (Mejri 10).
Assists_ Boston 28 (Thomas 8), Dallas 21 (Curry, Ferrell 5). Total
Fouls_ Boston 25, Dallas 16. Technicals_ Williams 2. Ejected_ Williams.
A_ 20,159 (19,200).