BORMIO, Italy (AP) Tom Dumoulin's overall lead in the Giro d'Italia was drastically reduced in the race's toughest stage Tuesday after the Dutchman stopped to answer the call of nature at the foot of the last of three major climbs.
Defending champion Vincenzo Nibali of the Bahrain-Merida team won the 16th leg, which crossed the Mortirolo and Stelvio passes.
Just before the unprecedented ascent to the Umbrail pass in Switzerland, Dumoulin stopped at the side of the road, stripped off his pink jersey and hopped down into a ditch to take care of business. By the time Dumoulin got back on his bike, the Team Sunweb rider had already dropped far behind his rivals.
''I just had some problems,'' Dumoulin said. ''I started to feel it in the downhill of the Stelvio and I had to stop. Back on the bike I decided to fight and draw conclusions after the finish. I'm still in the maglia rosa (leader's pink jersey) but I'm above all very disappointed.''
Becoming the first Italian rider to win a stage in this year's race, Nibali edged Mikel Landa of Team Sky in a two-man sprint, with 2014 champion Nairo Quintana crossing third, 12 seconds behind.
Dumoulin finished more than two minutes back but maintained a 31 second lead over Quintana, while Nibali moved up from fourth to third overall, 1:12 behind.
Thibaut Pinot dropped from third to fourth and Ilnur Zakarin remained fifth.
Dumoulin entered the stage 2:41 ahead of Quintana. He took the lead by dominating an individual time trial in Stage 10 and then won Stage 14, which finished with a serious climb to Oropa.
While Dumoulin ordered his team to slow down and wait when Quintana fell in the previous stage, Nibali and Quintana didn't wait for him this time.
''I don't know. It's difficult to say,'' Dumoulin said when asked if his rivals should have waited. ''It was a racing situation and we were going full gas.''
While Dumoulin is considered the sport's faster rider in time trials, he still hasn't proven himself as an elite climber. His best Grand Tour finish was sixth in the 2015 Spanish Vuelta, a race he led until he cracked two stages from the end.
''This is not something I was hoping for and I also don't think it shows my level at the moment,'' Dumoulin said. ''I had good legs. But there's nothing to do about it. I'm disappointed about myself that I lost two minutes while not having bad legs or anything but just having a problem.''
The 222-kilometer (138-mile) route from Rovetta to Bormio first ascended the narrow Mortirolo then went over the Stelvio before concluding with the Umbrail pass on the Swiss side of the Stelvio.
Part of an early breakaway, Landa of Team Sky was first over the snow-covered Stelvio, which marked the three-week race's highest point at an altitude of 2,758 meters (9,049 feet).
After a technical descent featuring nearly 50 hairpin turns, there was hardly any flat ground before the final climb up the Umbrail, which lasted 13 kilometers (eight miles) at a gradient between 9 and 12 percent. Then it was another long, high-speed descent of 19 kilometers (12 miles) into Bormio, an Alpine village known for its thermal baths and World Cup skiing races.
Nibali attacked up the Umbrail and then showed off his downhill skills on the descent to catch Landa and take his 13th individual stage win at a Grand Tour after a ride of nearly 6 1/2 hours.
''It's the victory of a complete rider. I had to be consistent from start to finish in a long and difficult stage,'' Nibali said. ''At the end I had to be an aggressive climber, a good downhill rider and a sprinter.''
At the start of the stage, a moment of silence was observed for the victims of the suicide attack at an Ariana Grande show in Manchester, England, plus the death of ex-MotoGP champion Nicky Hayden, who was hit by a car while training on his bicycle.
Stage 17 on Wednesday is a 219-kilometer (136-mile) leg from Tirano to Canazei featuring three categorized climbs, followed by an even tougher stage through the Dolomites on Thursday.
The 100th Giro ends Sunday with an individual time trial in Milan that should favor Dumoulin.
''There are more difficult stages to come but Dumoulin also has a time trial to his advantage in Milan,'' Nibali said.