The Samoan, who moved to Northampton from Ospreys this summer, put in a 40-minute performance full of flair, setting up a try for GJ van Velze before being replaced at the break.
Gareth Denman was another to enjoy a good debut, getting himself on the scoresheet during the second half, and another new man, Rob Verbakel, also got some game time.
In the end it was a convincing win for Saints as scores from Ben Nutley, Jamie Elliott, van Velze, Ben Foden, Denman and Tom Collins as well as a penalty try did the trick.
James Wilson added eight points with the boot, impressing at fly-half in the absence of England man Stephen Myler.
Bedford’s headline act was full-back Mark Atkinson, who scored a first-half hat-trick, but his efforts were in vain as Saints scored 26 unanswered points in the second half to secure the victory.
It was a perfect start to pre-season for Jim Mallinder’s men, who face games against Moseley and Edinburgh next week before a final friendly, at Leinster on August 30.
The presence of Fotuali’i is sure to boost gates for those games, with the scrum-half illustrating his vast skill-set in the first half at Goldington Road.
The No.9 and his new-team-mates, donning a striking new lime green kit, begun the game in bright fashion, with England star Foden providing plenty of spark from full-back.
And after a trademark push from the pack, Nutley, who looked in good shape during his 40 minutes on the pitch, dotted the ball down.
Wilson stepped up to the tee for the conversion, but fired his effort wide.
It didn’t take long for Bedford to restore parity, though, as they set up camp in the Saints 22 before Atkinson flew over in the corner.
Fly-half Jake Sharp made a better fist of adding the extras than Wilson had at the other end and Blues led 7-5 with 10 minutes gone.
But the Championship outfit weren’t in the ascendancy for long as good hands from Luther Burrell and Nutley sent Elliott over in the corner.
Wilson slotted the simple conversion and Saints then started to step it up in the scrum once again, turning the screw on the Bedford pack.
Burrell nearly forced the hosts into a mistake with a monstrous hit and Fotuali’i was showing strength and subtelty to keep his new team on the front foot.
The Samoan’s flair was unlocking doors in the Bedford defence and van Velze soon profited, carshing over for Saints’ third try.
Wilson, looking the part at fly-half, extended the lead to 19-7 but Bedford and Atkinson were refusing to be overawed, and the No.15 added his and the Blues’ second try before the break.
Sharp reduced the deficit to five points and the No.10 was causing problems for the away backline, starting the move that saw Atkinson dive over to register a first-half hat-trick.
Saints, 21-19 down at the break, made a host of changes, replacing their entire pack and bringing on Ryan Glynn for Fotuali’i.
But one man who remained on the pitch was Foden and he put his side back in front at the start of the second half, scootting round the outside of Bedford’s defence to score.
Wilson made it 26-21 to the away team and that lead soon got even greater as summer recruit Denman jumped over the line.
Saints then swapped their entire backline, bar Glynn and Ken Pisi, and two of the new men combined to add another try to the burgeoning tally.
Tom Stephenson took advantage of a turnover and sent Tom Collins clear, with the speedster needing no invitation to get his name on the scoresheet.
Harry Mallinder, son of Saints boss Jim, fired the conversion wide, but he soon got some points, adding the extras to a penalty try, earned by his side’s powerful pack.
It was the final try of an entertaining night and Saints’ strong second-half showing set them up for the tougher tests that lie in wait before the big kick-off on September 7.
Saints: Foden (Collins 56); Elliott (Artemyev 56), G Pisi (Diggin 56), Burrell (Stephenson 56), K Pisi (Glynn 70); Wilson (Mallinder 56), Fotuali’i (A Day 40); E Waller (A Waller 40), McMillan (Haywood 40), Mercey (Denman 40); Craig (Lawes 40), Verbakel (C Day 40); Dowson (Clark 40), Nutley (Harrison 40), van Velze (Dickinson 40).
Bedford Blues: Atkinson; Hircock, Burke, Dodge, Edwards; Sharp, Veenendaal; Fearn, Clare, Boulton; Howard, Gulliver; Armes, Fox, Vandermolen.
Replacements: Steenkamp, Cooper, Tupai, Harding, Stanley, Tapley, Lord, Jubb, Calder, Le Bourgeois, Adamson.