A year ago this week, Barcelona became the first team to overturn a 4-0 first-leg deficit in the Champions League knockout stage when beating PSG 6-1.
Porto, the Portuguese league leader, had to go one better but Klopp's decision to field a strong team rendered that unlikely scenario even more inconceivable.
Those fringe players that did come in for Liverpool — Adam Lallana and Alberto Moreno being two of them — had the carrot of staking a claim for a place in the team for Saturday's big Premier League match against Manchester United.
And it was the hosts who had the better of the chances, with Mane hooking a volley over the bar and then striking a low shot against the post in a subdued first half.
Roberto Firmino ran clear but ended up having a shot blocked on the hour, before immediately being taken off by Klopp as Liverpool's main striker was protected ahead of the United game.
Porto pressed late on but to no avail, as it failed to collect a first away win over an English opponent in the Champions League at the 13th attempt.