This first Ashes Test has shown a remarkable capacity for making rapid nonsense of the most reasoned assessment, but England looked to have the edge as the fourth day closed with Australia 174 for 6 in their pursuit of 311 to win.

All of Australia's specialist batsmen have gone, but first-innings debutant hero Ashton Agar and the experienced Brad Haddin are the not-out batsmen, with further batting competence to come.

"It has been pretty crazy," said Australia's captain Michael Clarke. "There's some more fight left in us for tomorrow."

Clarke also defused a potential controversy over the umpiring, which has been undistinguished, and the Decision Review System (DRS) used to resolve contested calls. Clearly unlucky on Friday when Stuart Broad was given not out after obviously hitting the ball, Australia had no more fortune against Broad as a bowler. Two contentious calls went against them, leaving them with no reviews for today's closing stages.

But Clarke, one of the batsmen affected, said: "We're using the DRS and it is the same for both teams. We've got no excuses at the moment."

This wildly fluctuating contest shifted back towards England at the precise mid-point of another sweltering, gripping day.

Australia had won the first half, first removing England's last four second-innings wickets for a further 49 runs then beginning their pursuit with vigour and purpose, reaching 84 without loss at exactly 3.5 runs an over.

Then play stopped for that mid-point drinks break between lunch and tea, and with the first ball afterwards Broad struck Shane Watson on the pad, roared his appeal and got the answer he wanted from umpire Aleem Dar. Watson called for a review, which showed the delivery would have clipped the edge of his leg stump, and was gone for 46.

Australia never really recovered momentum, scoring at less than two an over – 90 runs from 47 balls – over the rest of the day, while losing five more wickets.

Watson's successor Ed Cowan was also undone by an interval. On the stroke of tea he became Joe Root's first Test wicket, caught neatly at first slip for 14 by Jonathan Trott.

When Chris Rogers, playing in his second Test with the calm composure to be expected of a man who has scored 60 first-class hundreds, chipped Jimmy Anderson to Ian Bell at mid-wicket for 52, the scales were tilting towards England.

Clarke, Australia's best batsman, and Steve Smith, so impressive in the first innings, stopped the immediate slide. They added only 37 runs in just over 16 overs, but England batsman Ian Bell pointed out: "It's the sort of wicket where if two guys get in, it is extremely hard to get them out."

Then both fell to consecutive deliveries. England celebrated as if the Bastille fallen when Broad sent a delivery past Clarke's defensive shot to be caught behind by Matthew Prior. Umpire Dar was unconvinced and consulted colleague Kumar Dharmasena before raising his finger. Clarke, who had made 23, was confident he had not hit the ball and immediately called for a review.

But television umpire Marais Erasmus upheld the decision, costing Australia their most important wicket and their second review. That blow was compounded by the next ball when Swann had Smith lbw, and became crushing in the England spinner's next over. This time England reviewed a not-out from Dharmasena and Phil Hughes was out lbw. Three wickets had fallen for three runs, and at 164 for 6 the target looked extremely distant.

Earlier in the day, England's two overnight batsmen, Ian Bell and Broad, reached personal landmarks but neither was able to push much beyond as the innings, like England's first, ended in a clatter of wickets.

Broad, 45 not out overnight, completed his half-century with a slash through a gap in the slip cordon and dominated the early scoring, making it to 65 before he edged James Pattinson to Haddin.

Bell completed his century, his 18th and arguably best for England, with an opportunistic single after a push to cover was not stopped cleanly. He said: "It was my best Ashes innings. It was nice to put an important innings together when the team needed it most." He reached 109 before he edged Starc to Haddin.

Swann and Steve Finn followed in the space of three deliveries from the persevering Peter Siddle to end the innings at 375.

After looking set to end in three days, this match will go into a fifth where a sell-out crowd will be torn between conflicting desires to see England win and to experience more of the rollercoaster excitement that has already made it such an extraordinary contest.