No margin for error: A four-way tussle in the Giro d'Italia's grand finale

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Three weeks of the Giro d'Italia come down to this: 53 seconds, four riders, two mountains and one time trial. Just 48 hours from the finish in Milan, Nairo Quintana (Movistar), Tom Dumoulin (Sunweb), Vincenzo Nibali (Bahrain-Merida) and now Thibaut Pinot (FDJ) are all potential winners of the 100th edition of the corsa rosa. At this point, the margin for error is nil.

The Giro is delicately poised as it reaches its denouement. Quintana is just 38 seconds ahead of Dumoulin, 43 ahead of Nibali and 53 up on Pinot ahead of Saturday's penultimate stage over Monte Grappa and Foza to Asiago. With a 30-kilometre time trial to come in Milan the following afternoon, the Colombian knows that he must extend his buffer on stage 20 or risk being overhauled by Dumoulin – and perhaps Nibali and Pinot, too – at the death.

"We'll have to try to put time into Dumoulin in particular, because he's the strongest in the time trial," Quintana said on Friday.

Quintana will draw confidence from how Dumoulin suffered and lost more than a minute on Piancavallo on Friday. Less encouraging is that the fact that, the Blockhaus aside, Quintana's gains on this Giro have come through the weaknesses of his rivals rather than by virtue of his own strength.

"I had bad legs today, but I hope it was just today," Dumoulin said as he warmed down at the finish of stage 19, still wearing the pink jersey he had just surrendered to Quintana. "I don't know how they'll be tomorrow. I just hope they're better."

The pessimist says that three weeks of racing have finally caught up with Dumoulin, and his decline is terminal. A more optimistic viewpoint is that the Dutchman limited his losses gamely on his worst day of the race, and remains firmly poised to win the race overall in the final time trial.