MULTAN, Pakistan :Joe Root smashed an unbeaten century after overtaking Alastair Cook as England's top run-scorer in test cricket and guided the team to 351-3 at tea on the third day of their opening match against Pakistan on Wednesday.Root began the day on 32 not out, needing a further 39 runs to eclipse Cook's tally of 12,472, and the former captain eased to his target with an on-drive for four off Aamer Jamal before soaking up loud applause from the travelling English fans.He then fought off cramps after lunch to bring up his 35th century with a reverse-sweep as England trailed by 205 runs when the session ended with Root batting on 119 and Harry Brook not out on 64 after Ben Duckett's quick-fire 84.Root got to his fifty earlier with an inside edge and the 33-year-old survived a loud lbw appeal to go past Cook's record and into the top-five in the all-time list behind Rahul Dravid, Jacques Kallis, Ricky Ponting and Sachin Tendulkar.Resuming on 96-1 after Pakistan amassed 556 in their first innings on a flat pitch at the Multan Cricket Stadium, England lost Zak Crawley for 78 inside the first hour when the opener flicked one from Shaheen Afridi to Aamer Jamal at mid-wicket.That abruptly ended the 109-run stand for the second wicket but England were in no mood to slow down.Duckett, who dislocated his left thumb while taking a catch and was unable to open on Tuesday, showed no signs of the issue as he took to the crease and smashed spinner Abrar Ahmed out of the attack temporarily with three boundaries in the 30th over.The left-hander needed only 45 balls to bring up his half-century but he was trapped lbw by Aamer in the afternoon session to leave England on 249-3.There would be no respite for Pakistan as Brook ensured