Bell had produced a fine knock of 72* in the first innings, but he threw away his wicket with an awful shot just before tea on day four to leave Australia needing six more to take a 2-0 series lead.
With showers forecast and his side 530 runs ahead, Australia captain Michael Clarke declared on 132-3 at the start of the day.
The weather has not yet intervened, but Clarke's decision to declare looked a good one straight away as England got their second innings off to a nightmare start.
Cook was tempted into attacking a short ball that he top-edged to fine-leg, where Brad Harris ran in to take a brilliant catch.
Things got worse for the tourists when fellow opener Michael Carberry departed to leave England on 20-2.
Both players made half-centuries before Pietersen (53) chopped onto his stumps to give Siddle his second wicket of the day - his third of the match.
Root continued to look in good nick following Pietersen's dismissal and reached tea unbeaten on 66 from 165 balls.
Bell also looked composed at the other end until he shanked a full toss from Steve Smith to Johnson, who made no mistake at mid-on.
Debutante Ben Stokes faced two balls without scoring before tea was called.
England's only hope of avoiding defeat now appears to be in the hands of the weather Gods, but, unfortunately for the tourists, the sky above the Adelaide Oval remains clear.