Arnaud Demare (Groupama-FDJ) won the bunch kick at the end of stage 8 Saturday in Bellinzona, where the peloton navigated six laps of a technical 21.5km circuit, bringing back the final breakaway survivors within kilometres of the finish.
A ballistic pace on the final lap saw the peloton strung out in single file, but with the help of teammates Greg Van Avermaet and Stefan Küng, Porte was well positioned near the front of the group and sprinted to 12th place to preserve his GC advantage.
"That was such a nervous and stressful stage," Porte said. "It looked like today went without any problems, but that's thanks to my fantastic team here. BMC Racing Team has been great all week and today was another impressive display from them to put me in a good position in the hectic finish. It was one of those days where you are just happy to get it over and done with."
Sunday's stage avoids the nearby mountains but is not entirely flat, either. At 34km it will provide a good challenge for Porte and the other GC contenders and a last opportunity to shake up the final GC podium.
"The race has gone really well so far, but it's not over until it's over," Porte said. "Nairo Quintana had a fantastic day yesterday, and I think he could easily have another good day tomorrow, likewise with Wilco Kelderman.
"You can't underestimate either of them, so if I am here tomorrow in the yellow jersey, I will be super happy. I have to be positive, though, and things have been going well so far, so fingers crossed."
Porte, who is a new father, said being in a position to win the race comes as a bit of surprise after missing Tirreno-Adriatico because if Illness. He hasn't raced since finishing third at Tour de Romandie in April.
"For me, after having my crash last year, I think I had a good Santos Tour Down Under, but the season has not been so super since, so to be here and to be time trialling for the win on the last day of the Tour de Suisse is a dream come true."
While Porte will be vying for the overall win, he tabbed teammate Kung, who led the race for four days earlier in the week, for Sunday's stage win.
"Stefan is in another league to everyone going into tomorrow," Porte said. "In the [stage 1] team time trial, he made the difference for us. He's an incredible engine, and he did another fantastic job today. I think he is the big favourite for tomorrow."