SAM Underhill produced a superb defensive shift in front of Eddie Jones but it was not enough to prevent Bath slipping to a 24-6 Aviva Premiership defeat against Northampton.

Underhill marked his debut for the club he joined from the Ospreys during the summer by making 23 tackles in a display that successfully launched his quest to continue as England's openside for the autumn series.

The 21-year-old won his first cap in Argentina in June when James Haskell was involved in the British and Irish Lions tour and is in contention to start in the back row when the Pumas visit Twickenham on November 11.

For all Underhill's efforts at Franklin's Gardens - he was replaced in the 68th minute after sustaining a neck injury - Bath suffered their first defeat of the season as Northampton picked up where they left off against Leicester last Saturday.

Further distance was placed between Saints and their collapse to Saracens in their Premiership opener and once again the physicality of their pack, led by the impressive Courtney Lawes, was the springboard for victory.

Lawes was at the helm in the absence of Dylan Hartley, who had been ruled out with a hand injury, and the England forward crossed for the night's opening try, lock David Ribbans stormed over twice and George North added the fourth to seal a comfortable bonus-point victory.

Northampton controlled the opening quarter and were rewarded by a third-minute try from their captain, who forced his way over close to the left touchline.

A crisp line-out offered the opportunity to attack on the 22 and when Michael Paterson found slippery wing Tom Collins sweeping across from the right, Bath's defence splintered and Lawes was through.

Saints continued to probe with Lawes prominent, but as the quarter wore on their grip on the match loosened as Bath began to spend greater time with the ball.

Two Rhys Priestland penalties, the second won at a dominant scrum, saw the lead change hands and despite losing skipper Matt Garvey to injury they began to thrive, assisted by knock-ons from Harry Mallinder and Paul Hill.

It was Northampton who finished the half stronger, however, and through a line-out drive finished when man-of-the-match Ribbans found no one at home at the heart of what should have been the Bath defence, they restored their lead.

Ribbans went over for his second in the 53rd minute, a line-out steal from Lawes enabling Saints to attack in a move given momentum by a muscular run from Luther Burrell, before the second row arrived to crash through the white shirts.

The bonus point was claimed with five minutes to go through keeping the ball alive, with North on hand to complete a move that saw Bath scramble backwards.