Southampton broke a 103-year-old club record by going 21 games unbeaten as Russell Martin celebrated his return to Swansea with a 3-1 success.
Che Adams, Will Smallbone and birthday boy Flynn Downes scored first-half goals as the Saints secured a Sky Bet Championship victory that should have been by a far greater margin.
Jamie Paterson gave Swansea brief hope in cutting the deficit to 2-1, but this was a sobering defeat for the hosts – their first in four games since losing at Southampton on Boxing Day.
Southampton have now eclipsed their best unbeaten run in all competitions since joining the Football League in 1920. They are 20 league games unbeaten, and 21 unbeaten in all competitions.
A sixth win in seven league games moves Southampton into second place, above Ipswich on goal difference before they meet Championship leaders Leicester on Monday.
Martin was given a warm welcome by Swansea fans on his return to the club he managed for two years and left last June.
Luke Williams, who worked as Martin’s assistant at MK Dons and Swansea, was in charge in the home dugout for the first time in the league.
Williams had started his reign with an FA Cup victory over Morecambe and a Championship draw at Birmingham, but this was a far tougher proposition against visitors unbeaten since September 23.
Southampton thrashed Swansea 5-0 at St Mary’s and could have matched that total inside the opening half-hour.
Adams volleyed an inviting opportunity wide before Carl Rushworth pushed Stuart Armstrong’s sixth-minute shot into the Scotland striker’s path for his ninth goal of the season.
Rushworth was the busiest man in Swansea, with several stops including a fantastic double save to deny Ryan Fraser and Adam Armstrong.
Swansea’s defence was breached again after 20 minutes, although there was more than a hint of offside about it.
Stuart Armstrong seemed well beyond the last home defender, but he was allowed to continue and his cross was converted by Smallbone from inside the six-yard box.
Josh Tymon had Swansea’s first effort, looping over from 20 yards, but Rushworth kept them in the contest by kicking away Adam Armstrong’s angled attempt at a post.
Southampton’s share of possession was over 80 per cent at times, but Swansea scored out of nowhere four minutes before the break.
Harrison Ashby’s cross ended in a collision between Saints goalkeeper Gavin Bazunu and Jamal Lowe.
The Swansea striker had possibly been offside, but the ball ran kindly to Liam Cullen and his centre was nodded home by Paterson.
Southampton restored their two-goal advantage on the stroke of half-time as former Swansea midfielder Downes fired home from 20 yards with the aid of a deflection.
Downes was celebrating his 25th birthday, but did not salute his first Saints goal out of respect for his former club.
The second period was a far quieter affair until Paterson struck the Saints woodwork twice in as many minutes.
Bazunu also thwarted substitute Yannick Bolasie from close range as Swansea finished strongly, but without success.
The managers
Swansea’s Luke Williams:
To follow…
Southampton’s Russell Martin:
To follow…
