Robertson said from where he was positioned, the penalty looked weak but the ref saw it otherwise, pinging defender Charlie Yexley.
Two Canadians, Oliver Coren and Jean-Michel Paulin, were in the Rovers' mix but Englishman Fahad Rwakarambwe was out injured.
Defender Blake Koolen was dropped to the reserves.
The Fergus Neil-captained Rovers have dropped to the second last rung of the table with just one victory, a draw and four losses - three on the trot.
Robertson reiterated the need for fans to manage their expectations.
"I'm not concerned. I don't think we're going to be in the relegation side," he said, emphasising their defeats, bar the 6-2 one to Wellington United here, were narrow.
Robertson captains Team Wellington who lost 3-0 to Auckland City FC in the first leg of the Oceania League match at Kiwitea St yesterday.