Set an improbable 531 to win when Australia declared its second innings at 132-3 just before play resumed on day four, England lost captain Alastair Cook (1) in the second over and struggled to 247-6 at stumps.
Root (87) and Kevin Pietersen (53) shared a defiant 111-run partnership and Ben Stokes contributed a valuable 28 batting at No. 6 to help England force the test into the last day its best hope of salvaging a draw with rain forecast for Monday.
Matt Prior was unbeaten on 31 at stumps and batting with Stuart Broad (22).
Despite the strong position, the forecast for rain will make the Australians nervous in Adelaide, where they failed to finish off South Africa by two wickets last November when Faf du Plessis batted all day to salvage a draw.
Prior also has form in the match-saving stakes, having forced a draw and salvaged the series with his unbeaten 110 against New Zealand on the last day at Eden Park in March.
His highest score since then is 47, however, and he had 0, 4, 0 in his first three innings of this series. The seventh-wicket pair also had some close shaves in the last few overs against the new ball, with Prior leaving a ball that narrowly missed his off stump and Broad being hit in the shoulder by a bouncer from Mitchell Johnson.
With the lights on in the gloomy, overcast conditions, and the crowd clap-clap-clapping in time with Johnson's run-up, the last few overs were menacing.
But vice-captain Prior resolutely hung on for the first time in the series and Broad stuck with him.
Root batted courageously as the top order crumbled but he fell short of his century when he played back to a Nathan Lyon delivery, edged onto his pad and wicketkeeper Brad Haddin dived forward to take the catch his 200th in test cricket.
He batted for more than three hours and faced 194 balls, hitting nine boundaries, to hold up the Australian charge. Despite the heavy cloud cover all day, there was none of the rain forecast for Sunday that hastened Australia's pre-play declaration. Storms were expected overnight.
Australia was desperate to wrap up the second test with a day to spare, as it did in the first test in Brisbane.
Cook's early departure, out hooking Johnson, and the dismissal of Michael Carberry, out hooking Siddle with the total at 20, were offset by the stand between Root and Pietersen England's first century partnership of the series.
The removal of Pietersen and Ian Bell (6) between lunch and tea was another massive setback for England.
Pietersen played onto his stumps and was dismissed by Siddle for the ninth time in his career more than any other bowler in test cricket. Bell, who scored a chanceless, unbeaten 72 to prop up England's first innings of 172, could barely believe he hit a rank full toss from part-time legspinner Steve Smith directly to Johnson at mid-on just before tea.
Root, other than flashing outside off stump twice in consecutive overs from Johnson, played with composure belying his age.
Promoted to bat at No. 3 after Jonathan Trott quit the tour with a stress-related illness following the 381-run first test defeat, the 22-year-old Root faced 165 balls until his innings finally ended.
The England middle and lower order has wilted in the face of some fearful fast bowling from Johnson in this series, including a spell of 5-12 off 18 balls from the Australian quick on Saturday, but was better equipped late Sunday.