With Australia needing to complete the highest-ever Test run chase at The Oval, Warner and Khawaja each posted half-centuries in the pair's best opening stand of the series on Sunday.
Warner went to tea unbeaten on 58 when rain stopped play midway through the second session on day four, with Khawaja not out on 69.
Crucially, Warner was able to get through two separate spells against the retiring Stuart Broad, in the last head-to-head battle between the veteran stars.
The left-hander drove Broad for four through the off side in the opening over, and later survived a chest-high beamer from James Anderson when he ran it down to third man.
After looking somewhat scratchy early, Warner scored quicker after lunch by going after Joe Root and at one point slog-sweeping him for four.
Warner's form has been regularly scrutinised on this tour, after making several starts without producing a statement score.
But if he is able to push Australia further towards victory at The Oval, it will almost certainly lock him in for his dream farewell retirement at the SCG in January.
Khawaja has looked even more composed than Warner, with his only moment of concern a short ball from Mark Wood that hit him on the back of the helmet.
With England's attack appearing otherwise unthreatening on a wicket that has slowed down significantly, the 36-year-old barely offered a chance at The Oval in the opening two sessions.
He also passed 5000 Test runs just before the rain delay, a remarkable feat given Khawaja's career looked over two years ago when he was yet to reach the 3000-run milestone.
After arriving in England determined to win their first Ashes series in the country in 22 years, Australia still need a monumental effort to score the remaining 249 runs and achieve the feat.
To win the match, Australia must complete the second-highest run-chase in their Test history and the eighth-best of all time.
Australia could also survive the final four sessions to win the series 2-1, with rain potentially set to play a part.
Warner and Khawaja's start came after an emotional morning at The Oval, with the grandstands full to offer Broad a standing ovation following Saturday night's retirement announcement.
After being given a guard of honour onto the field, Broad hooked Mitchell Starc's final ball of the first over for six.
It would be the last ball he faced in Test cricket, with Todd Murphy removing James Anderson lbw moments later to have England all out for 395.
The wicket took Murphy's figures for the innings to 4-110, while Starc finished with 4-100.
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