Andy Robertson complained "slack" Liverpool did not deserve more than a point from their Premier League stalemate with West Brom.
Liverpool went ahead in the first half on Sunday through Sadio Mane but were unable to secure the points with a second goal before Semi Ajayi equalised for the Baggies eight minutes from time, earning a 1-1 draw.
Jurgen Klopp's side had controlled the opening 45 minutes at Anfield with 81.8 per cent of the possession and 10 shots to West Brom's one, although only Mane's strike troubled the target.
The Reds failed to turn their dominance into goals after the break and were increasingly vulnerable on the counter-attack, as the visitors had a further four efforts, of which three hit the target - including Ajayi's header.
It was the first time Liverpool had dropped points from a winning position in a Premier League home game against a side in the bottom three since December 2016, and Robertson bemoaned an error-strewn display.
"When you go slack, you get what you deserve," Robertson told Sky Sports.
"We created a lot of chances in the first half and then in the second half it was as if we didn't want to do it again. We went slack.
"Every one of us made a mistake in the second half which can't happen. Credit to West Brom for the way they played the second half.
"We should be experienced enough to see it out and build on the 1-0. We should have been 2-0, 3-0, maybe 4-0 up at half-time.
"We were dominating and it was up to us to take the chances, but we also should be professional enough to win 1-0 if we have to. We will take the point and move on. We can't dwell on it but it's a huge disappointment."
The result gave new West Brom head coach Sam Allardyce a first point and continued his impressive recent record at Anfield.
His past four visits to the home of the Reds have come with different sides (Sunderland, Crystal Palace, Everton and now West Brom), but he has not lost any of them (W1 D3).
Indeed, Allardyce was in charge of Palace when Liverpool last lost at home in the Premier League - 2-1 in April 2017.
Robertson felt Liverpool needed to show greater professionalism against the pragmatic approach of an Allardyce side.
"When you come up against a Sam Allardyce team, you know they will stay in it and take the one chance they get," explained the Scotland defender.
"You know they will look to frustrate you and play the game down and hit you on the counter-attack. We didn't let them do that in the first half, but then they grow with confidence the longer it goes 1-0.
"I've been in a Championship team that has come up and you want to frustrate the big teams and get that one chance you can get and that's exactly what happened.
"Credit to them. They were great in the second half but we need to be so much more professional. We didn't do that enough and that is frustrating."