ESSEX batsman Alistair Cook helped take England to the brink of Ashes glory Down Under with his third century of the series during the final Test in Sydney.

The 25-year-old took his series tally to 766 runs, at an average of 127, from just seven innings with his latest breathtaking knock of 189.

The opener, whose place in the England team was under threat at the beginning of the Ashes, has now made one double hundred, two centuries and two fifties from the tour of Australia.

He may not get a chance to move closer to Wally Hammond's all-time Ashes record of 905 runs after England's batsmen continued to pile on the runs after he had sliced a drive to cover off Shane Watson.

Ian Bell registered his maiden hundred against Australia and Matt Prior remains unbeaten at the crease on 54 with the score standing at 488-7.

Cook survived a controversial moment when precariously placed on 99, after he nudged a ball from spinner Michael Beer to Phil Hughes at short leg. Despite the excited celebrations of the Australian team, including Hughes, TV replays clearly showed the ball bouncing several inches short of the fielder, earning Cook a reprieve.

He had earlier survived the walk back to the pavilion on 46 when he lofted a catch to mid-on, again off Beer, but umpire Billy Bowden called for clarification on a suspected no-ball and the replay showed the spinner had overstepped the mark.

England hold a lead of 208 heading into the fourth day's play, needing only to draw the match to win the series 2-1.