(Reuters) - Manchester United's tactical flexibility continued to serve them well as they extended their unbeaten Premier League run to 15 games with a 3-0 win at Leicester City on Sunday to ramp up the pressure on their rivals for a top-four finish.

Arsenal and Liverpool have faltered in recent weeks to slip out of title contention behind runaway leaders Chelsea but United have found some momentum and now trail the fourth-placed Gunners by two points and the Reds, who are fifth, by one.

After a poor start to the season United have gone under the radar in their 15-game unbeaten run. Led by master tactician Jose Mourinho and a squad of adaptable players it is the Old Trafford side's tactical flexibility that is aiding them.

Where Arsenal and Liverpool look devoid of a 'Plan B' if their slick, quick-passing style fails, sixth-placed United can successfully adapt if their initial plans prove fruitless.

United started lethargically against Leicester and struggled to exert any control during the opening 35 minutes before a system tweak produced immediate results.

Forward Marcus Rashford moved out to the wing and Henrikh Mkhitaryan was deployed in a central playmaking role behind central striker Zlatan Ibrahimovic.

Thereafter United were irresistible, with Mkhitaryan and Juan Mata in particular picking Leicester apart with ease as the visitors scored three goals in seven minutes either side of halftime.

TACTICAL NOUS

"We went with 4-4-2, the same system as they play," Mourinho, whose tactical nous has been attributed to many famous victories in the past, told Sky Sports.

"We tried not to give (central defenders Wes) Morgan and (Robert) Huth a two-against-one fight and target against with Zlatan. We tried to give more freedom to Zlatan by playing with Marcus Rashford.

"We were fine, we were quite stable but without the quality of possession and control we normally have. We changed and started finding more spaces and then the first goal comes.

"And when the first goal comes everything is easy for us."

Mkhitaryan was the main benefactor of the tactical change.

Having been peripheral for the first 35 minutes the Armenian went on to produce a man-of-the-match display like those that made him such a highly sought after player at Borussia Dortmund.

"When we are playing football, one-two passes are very easy no matter which position," Mkhitaryan told Sky Sports.

"We tried to change the formation during the game and that's not something that is new for us.

"In this game the manager thought it was better I play behind the striker. It was his decision and I agreed and I was trying to do my best."

(Reporting by Tom Hayward; editing by Ken Ferris)