The former Wildcat played a career-high 24 minutes, tallying a career-high nine points (on 4-11 shooting) to go along with five rebounds, four assists, and two steals.
However, the Celtics lost 91-74 to the Dallas Mavericks, ending their stint in Las Vegas Summer League.
In eight Summer League games (including Orlando), Allen averaged 3.0 points, 3.1 rebounds, and 1.6 assists per game while shooting 26.5 percent from the field and 0-6 from 3.
Brandon Ashley had five points and four rebounds in 17 minutes for the Mavericks.
Rondae Hollis-Jefferson notched his first double-double in Summer League, with 15 points and 13 rebounds in 26 minutes. The forward shot 5-10 from the field and 5-6 from the free throw line.
He also blocked this layup attempt by Lonzo Ball.
Semifinals are Sunday
No matter how the last two days of Las Vegas Summer League end, at least one Wildcat will leave the city as a champion — all four remaining teams in the tournament have an ex-Wildcat on their roster.
The semifinals are Sunday and here’s who will be participating:
Johnson and the Blazers take on Simmons and the Grizzlies at 3 p.m. PT (ESPN2).
York and the Lakers face Ashley and the Mavericks when that game ends. It will also be televised on ESPN2.
The championship game is Monday.
Follow Ryan Kelapire on Twitter at @RKelapire