Doha: Qatar's Al Sadd took a huge step towards the knockout stage of the 2018 AFC Champions League after a 4-0 home win over FC Nasaf of Uzbekistan in their Matchday Four encounter on Tuesday.   The hosts got off to a flying start and took the lead in the third minute, with midfield superstar Xavi diverting in Boualem Khoukhi's cross to score his first-ever AFC Champions League goal.   Al Sadd doubled their lead in the 16th minute and this time it was a defender who got on the scoresheet. Full-back Abdelkarim Hassan finished off a surging solo run from the halfway line with a fierce strike that left Nasaf keeper Sanjar Kuvvatov with no chance of saving.   Baghdad Bounedjah then gave the Qatari side a comfortable 3-0 cushion at half time, with the Algerian netting his fifth goal of the tournament with an acrobatic overhead kick in the 43rd minute.   Fellow Algerian Jugurtha Hamroun, who had provided the assist for Bounedjah, got a goal of his own in the 71st minute, smashing in a low shot past Kuuvatov to round off a quick counter-attack.   The big win sends Al Sadd to the top of Group C with nine points from four games, and leaves them needing four points to qualify for the Round of 16. They host bottom of the group Al Wasl on Matchday Five when Nasaf welcome Persepolis to Uzbekistan.   An Al Sadd win coupled with Nasaf failing to beat Persepolis would see the Qatari and Iranian sides advance with a game to spare.