Playing the final game of his illustrious career, former Australia international Kewell was unable to inspire his side to victory at AAMI Park, meaning the Heart are guaranteed to end the regular season bottom of the table.
Western Sydney, meanwhile, can look forward to a week off and a home semi-final after late goals from Brendan Santalab and Youssouf Hersi earned a hard-fought triumph.
Nikolai Topor-Stanley headed the Wanderers into a 27th-minute lead from Shinji Ono's free-kick, but the Heart swiftly levelled through Orlando Engelaar.
Ono smashed a penalty against the crossbar in the second half and it looked as though the visitors would be punished when Jason Hoffman put the Heart ahead with 18 minutes remaining.
However, Santalab replied, after appearing to get away with a push on centre-back Robbie Wielaert, and Hersi then rounded off the scoring in the 86th minute.
Western Sydney's victory was crucial given that Central Coast Mariners and Melbourne Victory also recorded victories on Saturday.
The Mariners delivered an impressive display to win 2-0 at Premier Plate winners Brisbane Roar and claim third spot, with Nick Fitzgerald and Anthony Caceres on target in the first half.
Victory cruised to a 4-1 triumph at 10-man Wellington Phoenix, with Archie Thompson's first-minute strike setting the tone.
James Troisi and Guilherme added further goals for Kevin Muscat's men prior to half-time, and Mark Milligan scored from the penalty spot in the 59th minute after Shaun Timmins had been sent off for bringing down Kosta Barbarouses.
A stunning late volley from Jeremy Brockie represented little consolation for Wellington, who end the season in ninth position.
Both the Mariners and the Victory will be at home for their respective elimination finals.
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