Marco Verratti was running the game in midfield, although the Italian was fortunate not to be sent off for a unsafe tackle on Joe Gomez midway through the first half.
"We have won the fair play league twice in England but we looked like butchers when you see the yellow cards we had".
But for all their pressure they could not crack their opponents, who used every trick in the book to take time out of the game when they were wobbling, and it was the hosts who had the best chance with Alisson saving Marquinos' header.
"I suppose they were in the lead and they were looking to waste time", Robertson told Sky Sports.
The former RB Leipzig midfielder came on in the second half against PSG in Liverpool's Champions League game on Wednesday, however he had no impact on the result.
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In Northern California, the searchers tried to keep their minds on the task rather than the tragic situation. Some 4,000 firefighters from throughout the state and the West battled the flames at the height of the fire.
"It was our last chance to show that we are capable of competing with a team like Liverpool, a team with an incredible mentality", said PSG coach Thomas Tuchel. "That was necessary against Liverpool and it was a big step forward for us".
PSG had been desperate to get Neymar and Kylian Mbappe back fit for this game after both had picked up injuries on worldwide duty last week.
Angel Di Maria forced an early save from Alisson and the goalkeeper was soon in action again, Neymar firing straight at his fellow Brazil global.
PSG had eight shots on goal, and Liverpool had just one.
Not everybody shone but the majority of PSG's star names lived up to their billing and produced some scintillating football at times - notably in the first half.
Polish referee Szymon Marciniak initially pointed for a corner, but having presumably received some advice from his fellow official behind the goal, changed his mind and awarded a penalty which Milner dispatched against a cacophony of whistles and jeers.
"We were not anxious about playing at home".