Captain Khawaja played a controlled unbeaten knock of 86 on Monday on a challenging Bellerive Oval wicket, to push the Bulls to the top of the standings ahead of the Warriors on run rate.
Queensland had to grind their way to 6-226 to earn victory with 2.5 overs to spare, after Tasmania could only manage only 223 off their 50 overs.
Batting at the top of the order, Khawaja impressed despite playing and missing on several occasions during a 128-ball innings on a green and slow wicket.
It continues some strong one-day cup form for Khawaja who has already hit two centuries this season in four matches.
Queensland will seek to end a six-year one-day cup drought when they welcome WA on November 26 for the competition decider.
The two sides haven't met in a one-day cup final since 2003/04.
Queensland secured a 26-run win over WA on the Gold Coast three weeks ago when the teams last met.
The Bulls briefly looked challenged at 5-137, but Khawaja and Jack Wildermuth (48) took the Bulls over the line with an 85-run stand for the sixth wicket.
Queensland made full use of winning the toss to take early wickets, as the home side slipped to 4-40, before their lower order managed to get the innings going.
Paceman Mark Steketee did most of the damage for Queensland with 3-33.
A 76-run stand for the seventh wicket between James Faulkner (30) and Gurinder Sandhu (51) was the highlight for Tigers.
The only other Tasmanian batsmen to make runs were rookie Mac Wright (46) and former Queenslander Simon Milenko (36).