O'Sullivan had already beaten Anthony Hamilton 4-2 in the third round earlier in the day.
Vahedi barely had chance to get on the board, with just one break of 55, in the second frame, to show for his efforts.
O'Sullivan racked up another century break to add to the one he potted against Hamilton, notching 131 in frame number three.
It was also one-way traffic for Neil Robertson, easing to a 4-0 win over Gerard Greene.
Shaun Murphy progressed, beating Dominic Dale 4-1, scoring breaks of 100 and 69.
Mark Selby edged past Zhao Xintong 4-3 in a close encounter, while Kyren Wilson defeated Ding Junhui 4-2.
Judd Trump admitted his performance was below par, but he still beat Stephen Maguire 4-1, and John Higgins came through a finely-balanced match against Luca Brecel 4-3.