There were no further alarms for England with Harry Brook unbeaten on 14 and captain Ben Stokes on 24 not out.
England had launched into Australia’s bowling post-lunch and rocketed to 239-2. Crawley led a partnership of 121 from 152 balls with Moeen Ali, then 109 from 86 with Root at tea in a partnership which would grow to 206.
Crawley scored 106 on his own in the middle session.
Ali showed his versatility by scoring 54 at No. 3
England has to win here to keep the series alive, and warned Australia beforehand that it would try to force a quick result because Saturday’s play may be lost to forecasted rain. If England doesn’t win, Australia will retain the Ashes.
With that in mind, England added an entertaining 178 runs after lunch from 25 overs at more than seven per over.
The Australians were befuddled, especially expensive Cummins. Mitchell Starc finished the day on 2-74.
England’s first 100 took 22.1 overs. The second 100 took 13.2 overs.
Ali came out of test retirement for the series as emergency spin cover, then volunteered to bat at No. 3 when Ollie Pope was injured out of the series. Ali made it his job to give Root and Brook distance from the new ball and excelled with his first test fifty in 4 1/2 years.
He was dropped on 53 but out one run later at 130-2 when he hit Starc in front of square and gave Usman Khawaja a two-hand diving catch.
That brought in Root, who smacked the first ball he faced from Starc to the boundary.
Crawley reached a streaky century with lots of edged shots from 93 balls, the second fastest by an England opener in test history. The only quicker one was his own off 86 balls last year in Pakistan.
He and Root were so comfortable on a slow pitch against an aging ball that they hit sixes close to the interval.
Root reverse-ramped Marsh over deep third and Crawley slog-swept Travis Head over cow corner.