The boyband slipped to number three with their version of Mandy. The second highest new entry came from Shane Richie with I'm Your Man at number two.
Girls Aloud dropped two places to number four and Michael Jackson saw his new single debut at number five.
Elsewhere, Jackson's Number Ones was toppled from the top of the album chart by Westlife's Turnaround.
Will's number one is the first from his forthcoming second album, Friday's Child.
Another TV talent show winner, Fame Academy's Alex Parks, saw her debut album, Introduction, enter the chart at number five.
The singles chart promises to get very interesting over the coming weeks as the race for the Christmas number one gets under way.