England were on the brink of winning the first Test against Australia after more umpiring controversy dogged the Ashes series opener at Trent Bridge on Saturday.Australia were 174 for six at stumps on the fourth day, still needing a further 137 runs to reach their victory target of 311 after they lost three wickets for three runs late in the day.No side has made more to win in the fourth innings of a Trent Bridge Test than England's 284 for six against New Zealand in 2004.But the fact teenage debutant Ashton Agar, who in Australia's first innings made 98, the highest score by a Test No 11, was still there was a warning to Ashes-holders England they had work left to do if they were to go 1-0 up in this five-match series.Brad Haddin was 11 not out and Agar, promoted to No.8, one not out."You never know what is going to happen in this game," Clarke told BBC Radio's Test Match Special after stumps."We need Ashton Agar to play the type of innings he played in the first dig. Brad Haddin looks solid too."The wicket is dead but the ball is reverse-swinging. We need to start well tomorrow (Sunday) morning and think positively," added star batsman Clarke, whose fall for 23 late on Saturday sparked a slump that saw Australia decline from 161 for three to 164 for six in the space of 18 balls.England captured the prize scalp of Clarke when Stuart Broad, himself at the centre of an umpiring row on Friday, had him caught by wicketkeeper Matt Prior for 23 off an excellent full-length delivery.Pakistan's Aleem Dar, the bowler's end umpire, checked with square leg colleague Kumar Dharmasena to see if the ball had carried.However, the Sri Lankan was unable to give that confirmation and the on-field duo referred the decision to third umpire Marais Erasmus.Replays showed clearly that Prior had taken a clean catch and Clarke was given out by Dar. But the batsman immediately challenged the decision.Again the verdict was passed to South Africa's Erasmus and, with Hot Spot technology showing the ball had nicked the bat, Dar once more raised his finger.Australia had now used up all their reviews and next ball Steven Smith was lbw to Graeme Swann as the off-spinner, like Broad bowling on his Nottinghamshire home ground, extracted sharp turn.Left-hander Phil Hughes, playing back to another sharply spun Swann delivery, was initially given not out on nought by Dharmasena.This time England challenged the call and, with the Decision Review System showing the ball had just pitched in line before striking the batsman plumb in front of his stumps on the back leg, Hughes was out for a duck to the raucous delight of most of a 17,000 capacity sun-drenched crowd.Australia had frustrated England before opener Shane Watson was lbw to a Broad inswinger for 46.Watson challenged the verdict but, with replays indicating the ball would have clipped leg stump, the decision was upheld.Then to what became the last ball before tea, Ed Cowan edged part-time spinner Joe Root to Jonathan Trott at slip.Before tea Chris Rogers, playing his second Test five years after his debut, completed a maiden Test fifty off 104 balls with eight fours.But soon after tea, Rogers tamely chipped James Anderson to Ian Bell at midwicket.Earlier, Bell's 109 had been the cornerstone of England's second innings 375.Bell, 95 not out overnight, shared a seventh-wicket partnership of 138 with Broad (65).All-rounder Broad was controversially given not out on 37 on Friday despite edging Agar to Clarke at slip, a decision Australia couldn't challenge as by then they'd used up both their innings reviews."It is great to put together an innings when your team needs you to put you in a position to hopefully win a Test match," said Bell."It was definitely my number one Ashes innings so far. Every Test match you play you want to construct the right innings at the right time and that's what I managed to do on this occasion."