Peter Siddle grabbed the crucial breakthrough, ending England's first century partnership of the series when he bowled Pietersen for 53 off an inside edge.
And shortly before tea, Bell was on his way back to the dressing room for six after playing an injudicious shot off part-time leg-spinner Steve Smith.
Pietersen put on 111 runs for the third wicket with Joe Root after the tourists lost openers Alastair Cook and Michael Carberry cheaply in the morning session.
It was the ninth time Siddle has dismissed Pietersen in Tests, including twice in this match.
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At tea, England, chasing an unlikely target of 531 runs to win and prevent Australia from taking a decisive 2-0 lead in the five-Test series, were 143 for four.
Root, batting with authority at number three in the enforced absence of Jonathan Trott with a stress illness, was unbeaten on 66 with Ben Stokes yet to score.
Senior batsman Bell hung his head after hitting a Smith full-toss to man of the moment Mitchell Johnson, who took a sprawling catch at mid-on. Bell had top-scored with an unbeaten 72 in England's first innings of 172.