Jurgen Klopp accused Brentford of "stretching the rules" after Liverpool fell to a shock 3-1 defeat against the Bees on Monday.
An Ibrahima Konate own goal and a Yoane Wissa header put Liverpool two goals down before half-time, as Klopp's side struggled to cope with Brentford's set-piece deliveries.
Liverpool made three changes at the break – including Virgil van Dijk coming off – and the alterations looked to have given the Reds hope when Alex Oxlade-Chamberlain pulled a goal back on his 100th Premier League appearance for the club.
However, Bryan Mbeumo put the game to bed when he muscled Konate off the ball before lashing home late on to give Brentford their first win over Liverpool since 1938.
Klopp was frustrated after a game in which he perceived Brentford to have bent the rules, while he criticised referee Stuart Attwell's failure to take action over their behaviour during set-pieces.
"I'm not sure you can really control it all the time because each corner is a massive threat," Klopp told Sky Sports. "They stretch the rules in these moments with full body contact.
"There was only one offensive foul on a set-piece tonight which was whistled and that was against us, which is really funny. Holding is holding, and pushing is pushing.
"It was more the game they wanted than the one we wanted. They could dictate it because of how it got whistled.
"The two corners they scored with, one was offside and the other one, of course we don't behave perfectly, but they stretch rules. They are really pushing, they are really holding. That's obviously what you can do.
"The third goal I can really not respect. The ref thought it wasn't a foul and then VAR hides behind the phrase 'clear and obvious'. The referee has to explain that, if anybody could ask him.
"There's a reason why they are so successful with offensive set-pieces and still concede a lot of defensive goals around set-pieces, because there you cannot do the same stuff because in your own box, it would be a penalty."
While Klopp was angered by the officiating, he did not excuse his team from criticism, saying: "We have to point at ourselves. In the end, you don't lose a game if you do everything right. We did, for sure, not everything right.
"We are very critical of ourselves, and rightly so tonight. There were moments where we could have changed the game."
Darwin Nunez missed a golden opportunity to give Liverpool an early lead, rounding David Raya only to be denied by Ben Mee's goal-line block. No player has missed more big chances in the Premier League this season than Nunez's 15.
Klopp lamented his side's wastefulness in front of goal, adding: "We concede the first goal when we should already be 2-0 up, with super chances from Darwin and from Kostas [Tsimikas]. Darwin Nunez doesn't expect Ben Mee sliding there.
"In the next situation, they play a ball behind the line and we are not there, that's a massive point for criticism."