Tottenham coach Mauricio Pochettino bemoaned the award of the "soft" penalty that put Liverpool 2-0 up as they went on to seal a 3-0 victory at White Hart Lane.
Steven Gerrard scored from the spot after Joe Allen was adjudged to have been fouled by Eric Dier, with his effort sandwiched by goals from Raheem Sterling and Alberto Moreno.
It was Pochettino's first defeat since taking over at White Hart Lane, and he told Sky Sports: "Today was a very tough day for us.
"I think the key to our defeat was the start of the second half, when there was a soft penalty.
"We played OK, but were unlucky in the key moments -- but we need to improve. We need to build our confidence and build our future.
"We have a lot of games ahead. Sometimes you improve from your victories but you need to improve too from your defeats.
"At 2-0 down we tried -- we tried but were unlucky. I'm disappointed with the result."