Arsenal manager Arsene Wenger said it was "very difficult to understand" why Aaron Ramsey's first-half goal against Liverpool was ruled out.
Arsenal played out a 0-0 draw with Liverpool on Monday, with goalkeeper Petr Cech in particularly good form as the Gunners struggled in the first 45 minutes.
The home side at Emirates Stadium thought they had taken the lead early in the first half when Ramsey slotted past keeper Simon Mignolet, but the linesman flagged for offside.
"Liverpool had some chances in the first half and nothing in the second. We had chances in both halves and were unlucky because we scored a regular goal that was ruled out and that was very difficult to understand," Wenger told Sky Sports.
"It was in a period of the game when we had the most problems defensively but it is a regular goal, I cant see why it was cancelled -- it was clear.
"I didn't ask for an explanation, what does it change? It is about decision making and they got it wrong, I could see live that he could not be offside."
Wenger also hailed Cech and conceded it has been an average start to their Premier League campaign.
Cech made a point-blank stop to deny Christian Benteke and also tipped a Philippe Coutinho strike onto the post as Liverpool dominated the first half.
It was roles reversed after the break as Arsenal looked the more likely to take the three points, but a fifth home game in six without a goal meant they had to settle for the draw.
"We have started very average I must concede," Wenger said after the game. "We have four points from two homes games and won the most difficult game away from home.
"I think sharpness is missing a little bit in some players. I would like to give credit to Liverpool, they defended well and were quick to close us down.
"With the domination we had in the second half if you don't score the first goal the other team doesn't come out."
Wenger went into the game with both first-choice centre-backs sidelined as Per Mertesacker missed out through illness and Laurent Koscielny was absent with a back complaint.
Calum Chambers and Gabriel were thrown together, with the former struggling against Benteke and Coutinho in the first half -- although Wenger praised his defence for keeping a clean sheet.
He said: "I believe they have not the experience to play together, they have come in from one day to the next but overall we didn't concede and Petr Cech saved us two or three times in the first half -- during that period he was outstanding.
"Second half I think we should have won the game, we were a bit unlucky, we lack still a little bit physically and collectively to finish well what we start. Our game is still not fluent enough in the final third."
Information from Press Association was used in this report.