Xhaka took aim from 25 yards out on 56 minutes and beat Simon Mignolet to tie the scoreline- although the keeper should have done better - before Mesut Ozil's deft finish on 58 minutes put Arsenal ahead.
Their two-goal lead was short-lived, though, as a resurgent Arsenal were in front with three goals inside five remarkable minutes.
He said: "We didn't do ourselves justice in the first half".
Liverpool controlled the first-half, going into the break a goal to the good but in truth the Reds' should have been out of sight.
Liverpool, in their lurid orange away kit, suffered an early blow when captain Jordan Henderson limped off injured.
This time it was Firmino who did the damage, beating Cech from the edge of the area with a stinging shot that the keeper palmed weakly into his own net.
James Milner has called on Liverpool to be "more boring" and see out games in the future.
Firmino's drive narrowly cleared the crossbar just after the half-hour mark and Cech then had to deny Salah after Koscielny's slip let the Egypt worldwide in, with Sadio Mane acrobatically turning the rebound over.
Gary Neville praised Philippe Coutinho's desire to get on the score sheet after the Liverpool FC midfielder broke the deadlock at Arsenal on Friday night.
However, only a minute later Alexis Sanchez gave the Gunners an immediate lifeline by heading home a lovely whipped cross from Hector Bellerin. Yet such was the poor nature of the defending on both sides that Liverpool managed to recover, although what this highlighted was how far they are behind Manchester City in points and quality.