Louis Meintjes, Dimension Data's leader for this Giro d'Italia, slipped to four and a half minutes behind new race leader Simon Yates (Mitchelton-Scott) after losing three and a half minutes on Thursday's sixth stage to Mount Etna.
Meintjes was dropped from the group of favourites with 10km to go. He fought hard to limit his losses but finished 32nd.
Meintjes went into the Giro as Dimension Data's leader, and while one bad day won't necessarily derail his GC challenge, teammate Ben O'Connor might have to be ready to step into the breach. O'Connor impressed at the Tour of the Alps in April, where he won a stage and the white jersey for best young rider.
O'Connor became Dimension Data's best-placed rider with a solid ride on Mount Etna. He is now 13th in the GC, 1:39 down on Yates, and almost three minutes ahead of Meintjes. He is also second in the best young rider competition, 16 seconds behind Richard Carapaz of Movistar.
"It was not an easy day – but Igor [Anton], Jaco [Venter] and Ryan [Gibbons] guided Louis and me until the base of Etna," O'Connor said in a team press release.
"It was a hard tempo for the first 12km, where I was left with the final 20 or so guys. Then for the final 6km, as it pitched up more steeply, the attacks flowed. I did my best not to jump, as I knew I would suffer if I followed immediately. With about 2.5km to go, I was detached, but kept my cool and tried to limit my losses, still hoping to maybe grab the white jersey.
"I just missed it, sadly, but it's certainly within reach later in the week, and really I'm so pleased to be up there with the best again on one of the most iconic climbs around, and in the Giro d'Italia."
Meintjes and O'Connor will have further opportunities to show their form on the uphill finish to Montevergine on Saturday's stage 8, ahead of the considerably tougher ninth stage from Pesco Sannita to the summit finish at Gran Sasso d'Italia on Sunday.