The hosts at Liberty Stadium dominated the first half but were unable to capitalise, before being undone by a second-half Jordan Henderson goal.
Monk, whose team sit ninth in the Premier League after back-to-back losses, felt they had let a big chance slip.
"It was a good opportunity where we could have got something," he told Sky Sports.
"We dictated the whole of the first half, but we should have got the goal. Credit to Liverpool, they showed their quality in the second half.
"To concede the goal we did was very hard on the players. Against these big teams, you have to take that opportunity and get that goal or two.
"We've been doing that well this season but Liverpool stepped up second half and we weren't as crisp or sharp with our passes."
Bafetimbi Gomis and Gylfi Sigurdsson both had chances in the first half, with Liverpool goalkeeper Simon Mignolet needed to keep his side on level terms.
Brendan Rodgers' men pounced in the 68th minute, when Jordi Amat's clearance hit Henderson and beat Lukasz Fabianski.
Monk added: "Ultimately, we deserved at least a point from the game. The commitment and effort from my players was fantastic
"If we play like we did in the first half, we'll be able to get lots more points in the games to come."
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