Northampton Town, without a win in their last seven matches needed plenty to run in their favour if they were to create an upset. Yet they failed to test Antti Niemi throughout the entire 90 minutes.
Ultimately, some slick top-quality Premiership finishing gave Steve Wigley his first victory since taking over at the helm, and his side are viewing a similar run towards the fifth round, which they reached last season.
The Cobblers needed to heed the early warning signs, with Fabrice Fernandes striking a post in the fifth minute but the home side's best spell then almost produced the goal they were looking for to unsettle the Premiership outfit.
Scott McGleish headed wide in the 15th minute and then stretched for a volley from an Eric Sabin cross, but couldn't keep the ball down before the same player teed up Tom Youngs in the 27th minute for an opening which turned into a pivotal point.
Youngs just hesitated a moment too long with just Niemi to beat and the challenge of Andreas Jakobsson sent his shot over the crossbar.
The significance of that was confirmed five minutes later when Kevin Phillips fired the Saints ahead, sweeping home a Fernandes cross and it was 2-0 in the 35th minute when David Prutton executed a brilliant left-foot volley from 25 yards.
The second half turned into an anti-climax with the home side unable to offer a serious way back and, after Jelle Van Damme had tested Paul Rachubka with a fierce 49th minute drive, Neil McCann had wrapped things up in the 65th minute.
He was sent clear by a Phillips pass and coolly converted his chance as Rachubka came out to meet him.
Saints could have added a fourth, but Rory Delap's 25-yard drive was pushed away by Cobblers keeper Rachubka.