The Citizens used a striker-less approach to stun the Red Devils in the first half at Old Trafford on Tuesday evening, reports Efe news.
Rodrigo and Ilkay Gundogan were the only attacking players assigned to a set spot on the field, while Mahrez, De Bruyne, Raheem Sterling and Silva, who opened the scoring in the 17th minute with a curling strike from outside the penalty box, roved freely and wreaked havoc on the rival club's defensive lines.
Algeria's Mahrez, who was a finalist for the 2019 African Player of the Year award along with Egypt's Mohamed Salah and eventual winner Sadio Mane of Senegal, was involved in his 15th goal of the season (six goals and nine assists) when he maneuvered around goalie David De Gea and booted the ball into an empty net in the 33rd minute.
Pep Guardiola's men then continued to fire on all cylinders with a 2-0 lead, making the most of their numerical and positional advantage on attack and collectively posting a 91 percent pass accuracy in the first half.
The visitors' wingers also played a key role, providing support in the middle of the field that neutralised the efforts of Manchester United midfielders Fred and Andreas Pereira and defenders Phil Jones and Victor Lindelof to gain possession and get the ball going the other way.
When the home side managed to penetrate into the final third of the field or try to rattle their opponents with a high press, Man City made them pay the price by exploiting spaces in transition.
Case in point was the beautifully constructed third goal of the contest, when the Citizens executed a series of passes in a rapid counter-attack that was capped off by De Bruyne, who faked Jones out of his cleats before firing a shot that was saved by De Gea and then went into the goal off of Pereira's right foot.
The decision to substitute Jesse Lingard for Nemanja Matic at the start of the second half bolstered the midfield play of the home squad, who pulled one back in the 70th minute on Marcus Rashford's 17th goal of the season off a pass from 18-year-old sensation Mason Greenwood.
The goal was the fourth of Rashford's career against Manchester City.
The visitors continued to create scoring opportunities in the second half, but Sterling's inability to turn them into goals means that Man City will head into the Jan. 29 second-leg clash at Etihad Stadium with just a two-goal advantage.
The first leg of the other semifinal, which pits Leicester City against Aston Villa, will be played on Wednesday at King Power Stadium in Leicester.
The Carabao Cup, also known as the EFL Cup, is the secondary cup competition in England after the FA Cup.
( With inputs from IANS )