Northampton survived a late scare to snatch a narrow 35-34 victory over Newcastle at Kingston Park.
Thornbury and Spencer were both short-term signings, with Spencer already snapped up by Ospreys ahead of their round two EPCR Challenge Cup game this weekend.
Last season's Investec Champions Cup semi-finalists Northampton Saints got their new campaign off to a perfect start with a 38-8 bonus-point win over Castres at Franklin's Gardens.
Round six of the Gallagher Premiership promises to deliver another thrilling weekend of action, with teams looking to solidify their positions ahead of a break before the Test rugby returns in November.
Northampton Saints have handed a debut to England U20 international George Makepeace-Cubitt, who was playing in National League One last season for Rams Rugby.
Five England internationals are set to return to Northampton Saints’ line-up for their final pre-season match this Friday in the Mobbs Memorial Match.
England flew out of South Africa last Saturday evening to Heathrow as the rightful champions, the consistency of their potent scrum and manipulative defence helping them to a deserved first title since 2016.
Nathan Langdon has signed on with Northampton Saints ahead of the 2024/25 season, linking up with his brother Curtis, who has proved to be such a big hit at Franklin's Gardens.
Mark Mapletoft’s side demonstrated their ability to squeeze teams in that last four success, holding the Irish scoreless in the second half to win 31-20 after leading 22-20 at the interval.