Miguel Britos scored a controversial 93rd- minute equaliser for Watford as Liverpool were held in a thrilling game at Vicarage Road.
The Reds, without Barcelona target Philippe Coutinho due to a back injury, fell behind to Stefano Okaka's header.
Sadio Mane equalised with a clinical finish only for Abdoulaye Doucoure to restore the lead from close range.
Roberto Firmino's penalty made it 2-2 before Mohamed Salah thought he had won it only for Britos to bundle in.
In Jurgen Klopp's 100th competitive game as Reds boss, Liverpool wasted a string of chances before Uruguay defender Britos headed over the line from point blank range following a ricochet.
Watford keeper Heurelho Gomes, who conceded the penalty after hauling down Salah, denied Alberto Moreno with a fingertip save.
Joel Matip also hit the bar and Dejan Lovren forced another good save as the Reds dominated the closing stages until Watford's late leveller.
The six-goal thriller came on the back of Friday's opening match of the 2017-18campaign which produced seven goals as Arsenal beat Leicester 4-3.