Late tries from Alex Mitchell and Tom Collins helped Saints make it three wins from three in pre-season as they edged out Glasgow Warriors 19-14 in Stirling.
The youthful Warriors team had twice taken the lead, going 7-0 and 14-7 up.
But Saints kept going and managed to secure the victory thanks to scrum-half Mitchell and wing Collins.
Ahsee Tuala, who was making his first pre-season appearance, got the first try for Jim Mallinder's men.
Glasgow grabbed the lead after 10 minutes as Robbie Nairn set up George Horne, who dotted down.
Adam Hastings added the conversion and the home side continued to put Saints under pressure.
But the away side finally got going 20 minutes in as they started to turn up the heat on their hosts.
The momentum was briefly halted by a head injury for Saints fly-half Piers Francis, who was forced off.
But Saints continued to press and they used a set piece to launch an attack, which ended with replacement Harry Mallinder teeing up Tuala with a kick ahead, and the Samoan scored.
Mallinder converted to make it 7-7 at the break and Saints took the opportunity to switch their front row, with Alex Waller, Dylan Hartley and Kieran Brookes introduced.
It gave Hartley, who took over the Saints captaincy this summer, the chance to get his first minutes under his belt ahead of the new season.
And Saints kept their foot on the gas as they searched for a second try.
However, it was Glasgow who scored next as they turned defence into attack and captain Adam Ashe raced in for a picturebook try.
Both sides continued to make plenty of changes and Saints were soon camped on the Glasgow line.
Eventually the pressure told as Mitchell breached the home defence, but the conversion was missed to leave Saints two points down.
Glasgow looked set to secure the win, but Collins was to have the final say as he sprinted in from 40 metres to score.
Mallinder added the gloss with the successful conversion.
Saints will now play one more match before the Aviva Premiership season starts against Saracens at Twickenham on September 2.
Ulster will be the visitors to Franklin's Gardens on Friday night as Mallinder's men bid to complete a blemish-free pre-season campaign.
Glasgow Warriors: Hughes (McDowell 21); Santo (Jones 40), Kelly (Beattie 51), Johnson, Nairn; Hastings, Horne (Shiel 51); Bhatti (Allan 44), Malcolm (Stewart 71), Rae; Peterson, Cummings; Fagerson (Burr 64), Smith (Fusaro 44 (Stokes 74)), Ashe (c) (Wynne 64).
Saints: Foden (c) (Furbank 66); Estelles (Elliott 54), Tuala, Burrell, Collins; Francis (Mallinder 29), Groom (Mitchell 56); Ma'afu (A Waller 40), Clare (Hartley 40), Ford-Robinson (Brookes 40); Ribbans, Craig; Gibson, Ludlam, Eadie (Harrison 54).