In their defence, Robertson stressed several players were still recovering from the effects of influenza and hadn't trained as well.
Striker Angus Kilkolly put the visitors ahead at Endeavour Park after just five minutes from a penalty kick but the hosts equalised through an own goal "in the last kick" before halftime.
Saul Halpin scored in the 53rd minute and Kilkolly scored Rovers' third in the 71st while Ben Sippola and Owen Parker-Price got on the scorecard for Suburbs.
"We should have won but didn't take an awful lot of opportunities," Robertson lamented, but added they were still in the hunt for four goals to eclipse the 81-goal feat of the 1996 Gisborne City team, although the record holders were competing in a 12-team league that winter as opposed to the 10-team one now.
He felt even though they would match the Greeks' points record it would still be a great feat.
Robertson said both penalties awarded on Saturday were justified, although there was no malice in the tackles in the box.
Despite the draw, he was happy and hoped training this week would be back to the usual intensity for the cup playoff.