He made a pullup jumper off that isolation play, triggering a big finish for Dallas' new playmaker.
Ellis scored 24 points, including 13 in the third quarter when Dallas took its first lead, and the Mavericks beat the Philadelphia 76ers 97-94 on Monday night.
Ellis had 19 points in the second half and added a game-high 10 assists and two of Dallas' 11 blocked shots.
''I don't think I was being aggressive enough in the first half,'' said Ellis, who has scored at least 18 points in all 11 games with the Mavericks, the longest streak to start a career in Dallas. ''We weren't clicking as a team. They took us out of our game.''
Two nights after a 37-point loss in New Orleans and playing without budding star Michael Carter-Williams for the fourth straight game because of a foot injury, the Sixers held the Mavericks scoreless for the first 5 minutes and led by 10 in the first half.
Even after losing its lead for good late in the third quarter, Philadelphia stayed close behind Evan Turner, Tony Wroten and some late 3-pointers from James Anderson.
Turner had 26 points, nine rebounds and seven assists while Wroten had 19 points and five steals.
The Sixers were down six with just 30 seconds left, but one of 20 Dallas turnovers kept them alive. The outcome wasn't settled until the Mavericks inbounded with 4.8 seconds left and Shawn Marion had a breakaway dunk that came just after the final buzzer, leaving the final margin at three.
''I thought we battled and showed a lot of heart to come back from arguably our worst performance in New Orleans, and we lost to a good team,'' Philadelphia coach Brett Brown said.
Dirk Nowitzki and Marion had 20 points apiece for the Mavericks, who began a stretch of seven of nine games in Dallas. Nowitzki had 10 rebounds, and Marion chipped in seven.
The Mavericks pulled even twice in the third quarter before finally taking their first lead when Vince Carter knocked the ball loose as Hollis Thompson was going up for a layup.
Jae Crowder ended up with the ball on a breakaway but gave it up to Marion for the dunk and a 70-69 Dallas lead with 1:44 remaining.
Philadelphia had the ball down just 90-87 in the fourth, but Samuel Dalembert had one of his three blocks on a drive by Turner.
Jose Calderon was wide open for a short jumper on the other end but passed before getting the ball back beyond the arc and hitting for a 93-87 lead. Calderon had 14 points and was 4 of 10 from long range.
Coming off the bench for the first time this season, Dalembert also had eight points and a game-high 14 rebounds.
''I explained the situation this morning,'' Dallas coach Rick Carlisle said. ''He was great about it. It's a case of a guy who didn't let that affect him. He came in and he was a big factor.''
Anderson finished with 14 points, including 3-of-7 shooting from 3-point range. Thaddeus Young struggled from the field at 6 of 18 but still finished with a double-double at 12 points and 11 rebounds. Spencer Hawes had 10 points and 11 boards.
The Sixers shot just 38 percent and made only 12 of 22 free throws, numbers best illustrated by a sequence of three missed shots, four missed free throws and four offensive rebounds all in the same possession when they trailed 86-81 midway through the fourth quarter.
''I think we played our hearts out,'' Turner said. ''Once again, we didn't help ourselves at the free-throw line but we just have to keep up the intensity.''
Ellis didn't get his first basket until the 2:12 mark of the second quarter. But it wasn't because he was missing. He was just 2 of 4 from the field before halftime.
Carlisle's move to replace Dalembert, his center, with Crowder, a forward, in the starting lineup backfired at first.
Crowder went 0 for 5 with two turnovers while Dallas went scoreless in the first 5 minutes before Nowitzki hit a baseline jumper after Marion rebounded a missed 3-pointer by Crowder, who scored two points on 1-of-8 shooting but did have six rebounds.
NOTES: Dallas rookie PG Shane Larkin made his NBA debut late in the first quarter, four months after breaking his right ankle in the final practice before summer league. He immediately had a steal, and his first assist was on a bucket by Nowitzki. He finished three points, three assists and three steals. . . . The teams combined for 12 missed shots to start the game before Turner hit a jump shot with 9:10 left in the first quarter.