Driving a Leyton House March, Capelli lapped the shortened street course that utilises Victoria Park and Wakefield Road in a best time of 43.28s.
It was enough to outpace fellow guest starts Stefan Johansson (Ferrari F156) and Pierluigi Martini (Minardi M189) to the honour of the quickest time.
The F1 machinery, which also included a second Ferrari F156, a Ferrari 412T, Benetton-BMW and a Beatrice Lola, proved the highlight of a busy festival.
A smattering of classic and modern machinery also took to the track across the two days, including an assortment of V8 Supercars from the past two decades.
With the F1 running technically a demonstration, the quickest official session saw Brenton Ramsay's Birrana Racing Reynard 94D Formula Holden record 45.8s to edge Trent Shirvington's Mygale M11 Formula 3 by just 0.3s.
David Towe (BMW M3) and Jordan Roddy (Jaguar XJS) were the two quickest in the Heritage Touring Cars section, while local Chris Smerdon topped the Burson Bathurst era V8s.
Organisers were left thrilled with the turnout of fans, who sweltered through 35 degree temperatures to see a slice of the action.
The festival also included F1 machinery being driven through the centre of the city earlier in the week, as well as the two-day Classic Adelaide Rally.
“It has been a great week in Adelaide and the town has come alive with more than 350 cars combined competing in the Shannons Classic Adelaide Rally and Victoria Park Sprint,” said event spokesperson Tim Possingham.
“The enormously competitive Classic Adelaide Rally went down to the wire with all three leading cars in contention going into the final stage of the event.
“The great response from competitors, major brands looking to use the event to promote their latest models and host guests – and most importantly the fans turning out in force at Victoria Park has ensured this was the best Adelaide Motorsport Festival yet.
“The warm embrace of the Formula One drivers and their cars has firmly entrenched that aspect of the event as a ‘must see' for fans young and old.
“The way everyone rushed to the fence when they were out was just like it was in the 1980s.”
Classic Adelaide was taken out by the Mazda RX-7 of Michael Busby and John Caldicott ahead of the Triumph TR7 of Craig Haysman/Julie Boorman and Toyota AE86 of Oscar Matthews/Darren Masters.
South Australian Supercars drivers Nick Percat (McLaren 570GT) and Todd Hazelwood (HSV GTS) took part in the event's Marque Tour section, while Tim Slade and Josh Kean drove in the Ferrari Spettacolo display.
Kean, who also piloted 1350bph BMW-powered Benneton in the Formula One sessions, lapped the Victoria Park circuit in the Ferrari F40GTE – one of only eight ever produced.
Slade, meanwhile, sampled the Ferrari 599 FXX at speed and had high praise for the entire event.
“It's cool to be here this weekend, driving some very cool cars on great roads,” said Slade.
“I've been to the Classic Adelaide Rally a lot with Dad so it was great to be part of it.
“I love being able to support South Australian events like this and the Clipsal 500.
“There's some great cars here and it's great to see how many people have come out to have a look. It's getting bigger and better every year.
“It caters to a whole variety of different people, because there's someone on the track and around the park for everyone.”