Monday night football! Arguably the biggest game of matchday 10 of the Premier League was played when Tottenham Hotspur hosted Manchester City at Wembley.It was an emotional night for a certain Riyad Mahrez, as his former Chairman at Leicester City, Vichai Srivaddhanaprabha, passed away in a tragic helicopter crash. Mahrez said, after the game against Spurs, that Mr. Srivaddhanaprabha was a father figure to him and his death was heartbreaking.But the emotions surely didn't affect the Algerian winger's performance on the night, as he proved to be the difference maker against Spurs.In the sixth minute of the match, a defensive slip-up from Kieran Trippier let Raheem Sterling have a run into the Spurs box. Mahrez was alert and on hand to dispatch the pass from Sterling into the back of the net.Arms pointing towards the heaven as a tribute to his former chairman, the Algerian international sealed all three points for the defending champions with that goal and sent them to the top of the Premier League table.As the commentators clearly pointed out during the game, 'once a Fox, now completely a Cityzen', Mahrez has lived up to his club-record price tag of £60 million and is clearly an integral part of Pep Guardiola's plans in the blue half of Manchester.Now over to the Red half of the city, and things have not been great for Manchester United. Clearly, nothing has gone according to the plan for Jose Mourinho and his men this season.While the team has collectively underperformed so far, one man has conspicuously failed to justify his big move to the Red Devils last January.Alexis Sanchez did score the all-important winner against Newcastle United this season but has not made a remarkable contribution to the Red Devils' cause otherwise.The Chilean international was linked to City multiple times and it appears the Cityzens have dodged a bullet and made a secure investment in Mahrez.This is why we will now discuss why Manchester United should have spent on wooing the former Leicester City man instead of Sanchez.#3 A solution to United's right wing problemsMahrez has been used well by GuardiolaWhile Jose Mourinho has bemoaned the fact that United did not make any defensive signings this summer, an area that he seems to have given the least attention to is the right flank of his team.Now, this is an area that the Red Devils should have strengthened a long time ago and still seem to neglect.Most of the time, Mourinho fills the area with Juan Mata, Jesse Lingard and Marcus Rashford. But they are not proper wingers and have a tendency to cut into the middle rather than hugging the touchline and delivering crosses on a regular basis.Mahrez has been stationed by Guardiola on the right wing and he plays a role where he stretches the opposition defences and allows the midfielders of Manchester City come into play as well.His gameplan has been so good that he has kept last season's PFA Young Player of the Year, Leroy Sane, out of the City starting XI.No player has completed more take-ons in a single Premier League game this season for Man City than Riyad Mahrez vs. Newcastle (4).A constant threat. 👏 pic.twitter.com/orQ2bZbzNu— Squawka Football (@Squawka) September 1, 2018The Algerian has scored four goals in the Premier League with his shots per game standing at an average of 2.4, overshadowing Sanchez's performance this season.Even when it comes to passing success rate and crosses delivered per game, Mahrez steals the march on Sanchez with 86% and 0.5 respectively.