Both scored tap-ins on Sunday at Coopers Stadium, extending Perth's unbeaten start to the season to three wins and a draw.

Irishman Keogh helped to deliver the Reds' first defeat of the season after finding his customary spot: right place, right time.

In the 73rd minute, United goalkeeper Paul Izzo produced a superb diving save to halt a fierce Alex Grant header, only for the rebound to fall to Keogh almost standing on the goal-line.

Keogh duly tapped in for his fourth goal in four games of the campaign.

And teammate Ikonomidis iced the win in the 90th minute after a neat combination, slotting into an unmarked goal after rounding Izzo.

The Glory take top billing with 10 points, two ahead of the only other unbeaten outfit, Sydney FC (two wins, two draws).

Perth largely made the running against Adelaide and could have won by more, with Joel Chianese and Keogh unable to convert early golden chances.

Chianese, in the 12 minute, was played in by Keogh but, after turning on his left foot, shot into the crossbar from inside 10 metres.

Keogh missed a swinging right-footer from five metres, some 10 minutes later, as the visitors found early attacking fluency.

Twice in the opening half, the video assistant referee (VAR) examined incidents in the Reds' attack.

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Initially, video checked that Ben Halloran wasn't brought down in the box in collision with Glory gloveman Liam Reddy.

And in the 39th minute, VAR - after a two-minute ruling - adjudged a shot which struck Perth defender Shane Lowry on an arm was outside the box.

Both interventions deservedly rejected penalty claims and Adelaide's loss was further soured by an injury to German midfielder Mirko Boland, who left the field in the second half clutching his left hamstring.