Many pundits had tipped the Whites to overcome visiting Sunderland, who had not won an away game in the Premier League this season prior to the trip to Craven Cottage.
However, following a red card that was handed to Fulham centre-back Brede Hangeland during the first half, the Black Cats went on to win the match by a two-goal margin.
"It was a hard game for us because it started very badly with the red card for Brede," Petric told the club's official website. "Then we were 1-0 down so it was good to come back and equalise, although they scored two minutes after my goal which was a pity.
"I think we have to learn from that game, but we had two injuries so I think that luck was not on our side."
Petric came off the bench to score Fulham's goal at the Cottage.