The Team Sky leader, who was third overall at last year's Giro, was dropped on the first climb of the day, the third-category Passo della Collina, which came just after 20 kilometres. He soon found himself over six minutes in arrears and climbed off just shy of the start of the second third-cat climb of Pietracolora over 30km later.
Team Sky doctor Inigo Sarriegui said Landa "woke up early this morning feeling unwell with abdominal pains" and was diagnosed with viral gastroenteritis.
He was well enough to start the stage but it soon became clear he was suffering physically. Teammates dropped back to try to pace him back to the bunch but, with teams like Astana understandably keen to kick on, the gap kept going out, and Landa was forced to climb into the team car, his first Grand Tour leadership berth ending dismally.
"Mikel was ill overnight but we spoke this morning and he started today's stage with the hope of being able to pull through," explained Sky principal Dave Brailsford. "It was pretty clear that the illness had badly affected him and that he wasn't going to be able to continue."
Landa's struggles were all the more shocking given the way he had surpassed all expectations in the stage nine time trial, which left him in a very promising position on GC - eighth and less than 30 seconds back on pre-race favourite Vincenzo Nibali (Astana).The 26-year-old was already feeling optimistic ahead of the mountains - his preferred terrain.
Team Sky's GC hopes are now a thing of the past, with Nicolas Roche their next best placed rider at 6:47 down on leader Gianluca Brambilla.
"We are really disappointed for Mikel, who was riding well and looking forward to attacking in the mountains and animating the race," added Brailsford.
"However, we came here as a team and we'll continue as a team. There is a long way still to go, and although our focus was on Mikel, there's plenty of time for us to still make an impact at this Giro"
- Giro d'Italia: Landa admits to 'not feeling great'
- Landa delighted with powerful time trial ride in Giro d'Italia
- Renewed optimism for Landa ahead of the mountains
- Giro rest-day: Analysing the GC contenders
Sky's Giro ordeals
In stark contrast to their fortunes in the Tour de France, where they have three wins in the last four editions, Team Sky have had a rough time at the Giro d'Italia over the years.
In 2013, Bradley Wiggins, the then Tour champion, went in as one of the big favourites but his race was over after a miserable 12 stages. Having struggled on the wet descents, seemingly losing his nerve, a chest infection eventually forced Wiggins out of the race. That Giro was not a complete disaster for Sky, however, as Rigoberto Urán stepped up to the plate to finish second overall.
In 2014, Sky went into the Giro d'Italia without a true overall contender. Dario Cataldo, who had finished 13th in 2011, was the rider with the most pedigree but it was 20-year-old neo-pro Sebastian Henao who secured the team's best placing with 22nd, almost an hour behind winner Nairo Quintana.
Last year, Richie Porte, central to Bradley Wiggins' and Chris Froome's Tour victories, was team leader and a bona fide favourite for the title, especially given his rich vein of form in the early part of the season.
However, suspicions that Porte lacked the ability to put everything together consistently over three weeks were borne out. After a great first week, the Australian suffered a series of setbacks, infamously being docked two minutes for an illegal wheel change with compatriot Simon Clarke. A disappointing result in the important time trial followed, as did a knee injury, and Porte abandoned after losing 27 minutes on the mountainous stage 15.