A bullish performance by Exeter tighthead Tomas Francis could trigger a tug-of-war between Stuart Lancaster and Warren Gatland after the 21st 2lb prop helped end Northampton’s three-month unbeaten run in the Aviva Premiership. Against a side who pride themselves on the set-piece, Francis dominated his scrummaging contest against Alex Corbisiero and put down a significant marker for his inclusion at the World Cup. The 22-year-old — who qualifies for both England and Wales — is yet to pledge his international allegiance, despite having been called up to Gatland’s training camp during the RBS 6 Nations. Dave Ewers (right) tackles Samu Manoa of Northampton Saints during the Aviva Premiership match . Chiefs prop Tomas Francis, who qualifies for England and Wales, impressed up against Alex Corbisiero . ‘Tomas is a young man and will only get better through regular exposure,’ said Exeter director of rugby Rob Baxter. ‘He’s been to a Welsh training camp, but he’s English.’ With Wales suffering from injury problems in the front row, Francis (right) could be fast-tracked through the ranks to face England in the World Cup pool match. But his performance at Sandy Park may tempt Lancaster to make a late move for the youngster, with Chiefs moving back into the play-off positions with three games to play. Christian Day (right) and Alex Corbisiero of Northampton drive at the Exeter defence during their defeat . Try-scorer Elliot is tackled by the Chiefs defence as they tried to start a comeback but weren't able to . Some suspected a Saints backlash following their European exit to Clermont Auvergne but a yellow mist descended and the champions paid the price for indiscipline and inaccuracy. With Calum Clark, Stephen Myler and Alex Waller all sin-binned within 15 minutes of each other, Exeter turned the screw and sent Northampton home empty handed. Exeter started sharply with Phil Dollman touching down before Northampton pulled back through James Wilson’s try. Mitch Lees (right) attempts to drive through Northampton number eight Dickinson at Sandy Park . Lees attempts to break a tackle of the Saints forwards as he helped his side to victory over Northampton . Henry Slade’s penalties and the Saints’ ill-discipline kept Exeter in charge before Francis’ pressure at the set-piece helped earn a penalty try. ‘They put our set piece — particularly our scrums — under pressure,’ said Saints director of rugby Jim Mallinder. Jamie Elliot dived over for a late try, but it was scant consolation for the travel-weary Northampton. Wasps' Tom Varndell on his way to a try hat-trick . Leigh may miss semi . Leigh Halfpenny could miss Toulon’s Champions Cup semi-final against Leinster after suffering a suspected dislocated shoulder during Saturday’s Top 14 victory over Grenoble. However, Saracens are confident fly-half Owen Farrell will recover from a knee injury in time for their semi-final against Clermont Auvergne. Winger Tom Varndell scored a hat-trick of tries as Wasps secured a bonus point 40-13 victory at London Welsh. Despite keeping their top-six hopes alive, Wasps director of rugby Dai Young warned: ‘We need to improve.’ Sale director of rugby Steve Diamond hit out at referee Greg Macdonald after a surprise 25-23 defeat at London Irish. ‘For the critical try just before half-time, their player was 15 metres offside,’ said Diamond.
Exeter moved up to fourth after completing a double over Northampton . Phil Dollman and a penalty try helped the Chiefs on their way to victory . James Wilson and Jamie Elliot scored for the Saints but to no avail .