The Portuguese side have a mountain to climb in the quarter-final tie as they currently find themselves 3-1 down against the six-time European champions ahead of the second leg at Anfield.
Liverpool were the superior side, especially in the first half, where they created a catalogue of chances.
Time and again they found space in dangerous areas thanks to their class all over the shop.
They well and truly won the midfield battle and Ashton singled out former QPR and Tottenham man Taarabt, who was taken off in the 70th minute.
"Taarabt, he's so far out of his depth in this game, honestly," Ashton said on commentary for talkSPORT.
"He's lost the ball five or six times. There's no energy to get back, whether that's mental or physically [I don't know].
"He looked like he was breathing heavily to try and get back into a defensive position.
"Julian Weigl is the only one of those Benfica midfielders that even remotely looks like he's got a defensive brain and even he's struggling to cope."
The deadlock was broken as Ibrahima Konate headed in his first goal for Liverpool on 17 minutes.
It was 2-0 on 34 minutes as Sadio Mane tapped into an empty net from six yards out having been teed up by Luis Diaz after Trent Alexander-Arnold did brilliantly to pick out the Colombian with a raking long ball.
Benfica pulled one back early in the second half as Darwin Nunez took advantage of a Konate mistake before clipping the ball past Reds goalkeeper Alisson.
But Liverpool are firmly in charge of the tie with Diaz netting late on - the Colombian latching onto Naby Keita's through ball before rounding Benfica goalkeeper Odysseas Vlachodimos.