"We keep saying to David he needs to be on the score sheet more often and he did well tonight," McMahon told Liverpoolfc.tv.
"Me and Antonio (Gomez Perez) lost a bet with him because we said if he scored tonight then Antonio would pay for the next meal we have out as a squad, so we are a little bit disappointed!
"I'm happy for David as he is always looking threatening and looking to score goals. It's always nice to be threatening whenever we go forward.
"We have a lot of good pace in the side and players that can cause problems for defenders.
"We played a lot of good stuff but we had a little bit of anger at the end because we conceded a goal. We switched off near the end when we conceded the penalty but overall we are really pleased."