Sanchez clattered into Diaz in the first half as the Liverpool striker headed home the first goal on 19 minutes.
Diaz beat Sanchez’s late lunge for the ball and the Albion keeper was totally out of control and poleaxed the Reds man as he followed through.
The medics were immediately waved on by referee Mike Dean, but a subsequent VAR review allowed the goalkeeper to controversially remain on the field.
Albion head coach Graham Potter said: “The quality of the run and pass beat him. I have not seen it back, I think it was an accident.
“It’s not a happy camp when you lose, but we just need to focus on the next game. The Premier League can be difficult. The recency of results is the lens you look at. Rightly so, but we need to do better.
“We need to get to the points tally we want, and the only way we can do that is to focus on the next game.”
On Diaz, Klopp added: “He’s top class. He’s come in and done fantastically well. With the ball, the quality he possesses, without it, his work rate, it was another big performance from him.”
On a potential red card for Robert Sanchez, the Anfield boss said: “I don’t know. He’s obviously late, but Luis has done so well to get there first. It was an important goal at the time; a big performance from him and the team.”
Liverpool added their second from the penalty spot in the 60th minute.
Dean had pointed to the spot after Naby Keita’s half-volley struck Bissouma on the arm.
Mohamed Salah stepped up to take the penalty and fired it past Sanchez and into the back of the net.
Check out the latest Premier League speculation below...
1. Roma keen on Gbamin
Everton midfielder Jean-Philippe Gbamin could end up making a shock move to Roma amid question marks over his loan spell at CSKA Moscow. (Daily Mail)
2. Gunners keen on Coutinho
Arsenal are reportedly monitoring Philippe Coutinho ‘s situation at Aston Villa with the view to hijacking a transfer. (Sport)
3. Worrall in demand
West Ham United and Everton are reportedly set to battle it out for the services of Nottingham Forest defender Joe Worrall in the summer. (The Sun)
4. Ostigard ‘wants to stay’
Genoa general manager Johannes Spors has insisted that Brighton and Hove Albion defender Leo Ostigard wants to stay at the club beyond his current loan deal. (CalcioMercato)