Defending champions defeated
Shock as Djokovic and Jamie Murray out
In what will be the upset of the tournament the 117th seed beat the six-times winner 7-6 5-7 2-6 7-6 6-4.
Istomin battled to victory in the Rod Laver Arena, defeating the world number two in four hours and 48 minutes.
The Serb has only lost to a player ranked outside the top 100 once in the past seven years – to Juan Martin del Potro at last year’s Olympics.
His defeat creates a huge opportunity for Andy Murray to lift the crown after five appearances as a losing finalist.
Defending doubles champions Jamie Murray and Brazilian partner Bruno Soares have been knocked out in the first round by Sam Querrey and Donald Young who took the match 6-3 7-6 (7-5).
American Querrey will be hoping to make it a double over the Murray brothers when he takes on Andy in the singles tomorrow.
Of the other Brits, Heather Watson lost 2-6 7-6 10-8 to qualifier Jennifer Brady after forfeiting five match points.
Johanna Konta beat Naomi Osaka 6-4 6-2 to reach third round. Kyle Edmund lost 6-2 6-4 6-2 to Pablo Carreno Busta.
Uncapped Edinburgh forwards Simon Berghan and Cornell du Preez are included but David Denton is unfit.
Alasdair Dickinson is also absent through injury, while fellow Edinburgh prop WP Nel is a doubt because of a neck problem.
Cotter will step down after the tournament to take over as Montpellier coach and will be replaced by Glasgow Warriors’ Gregor Townsend.
Forwards: Alex Allan, Zander Fagerson, Gordon Reid (all Glasgow Warriors), Simon Berghan, Allan Dell, Willem Nel (all Edinburgh Rugby), Jon Welsh (Newcastle Falcons), Fraser Brown (Glasgow Warriors), Ross Ford, Stuart McInally (both Edinburgh Rugby), Jonny Gray (Glasgow Warriors), Richie Gray (Toulouse), Grant Gilchrist (Edinburgh Rugby), Tim Swinson (Glasgow Warriors), Ben Toolis (Edinburgh Rugby), John Barclay (Scarlets), Cornell Du Preez, John Hardie, Hamish Watson (all Edinburgh Rugby), Rob Harley, Josh Strauss, Ryan Wilson (all Glasgow Warriors)
Backs: Greig Laidlaw (Gloucester), Ali Price, Henry Pyrgos, Finn Russell (all Glasgow Warriors), Duncan Weir (Edinburgh Rugby), Mark Bennett, Alex Dunbar (Glasgow Warriors), Huw Jones (Stormers), Matt Scott (Gloucester), Duncan Taylor (Saracens), Stuart Hogg (Glasgow Warriors), Damien Hoyland (Edinburgh Rugby), Sean Maitland (Saracens), Tommy Seymour (Glasgow Warriors), Tim Visser (Harlequins)
4 February – Scotland v Ireland (14:25)
12 February – France v Scotland (15:00)
25 February – Scotland v Wales (14:25)
11 March – England v Scotland (16:00)
18 March – Scotland v Italy (12:30)