Simon Yates had his Giro d'Italia lead halved on Thursday as Tom Dumoulin closed to within 28 seconds in a stage won by Maximilian Schachmann.
Yates was 56 seconds to the good overnight but struggled on the climb to the summit finish, while Dumoulin followed an attack by Chris Froome in the closing stages of stage 18, which took riders from Abbiategrasso to Prato Nevoso.
Mitchelton-Scott rider Yates has topped the general classification since stage six but is now under pressure from last year's winner with three stages to go.
Quick-Step Floors' Schachmann held off the challenge of Ruben Plaza to take his first Grand Tour stage victory, finishing 10 seconds clear.
Mattia Cattaneo was third for Androni Giocattoli-Sidermec, a further six seconds back.
The trio survived an early break to last the distance, with Plaza unable to match Schachmann's final attack.
PRESSURE ON FOR YATES
Having looked peerless so far during the Giro, the cracks have started to show for Yates.
A two-kilometre stretch saw 28 seconds shaved off his advantage, as he failed to track a late Froome attack.
Dumoulin followed to really turn up the heat on the Briton, while Domenico Pozzovivo also edged closer to Yates.
Pozzovivo now sits third in the GC, two minutes and 43 seconds adrift of the leader.
STAGE RESULT
1. Maximilian Schachmann (Quick-Step Floors) 4:55:42
2. Ruben Plaza (Israel Cycling Academy) +0:10
3. Mattia Cattaneo (Androni Giocattoli-Sidermec) +0:16
4. Christoph Pfingsten (Bora-Hansgrohe) + 1:10
5. Marco Marcato (UAE Team Emirates) 1:26
CLASSIFICATION STANDINGS
General Classification
1. Simon Yates (Mitchelton-Scott) 75:06:24
2. Tom Dumoulin (Team Sunweb) +0:28
3. Domenico Pozzovivo (Bahrain-Merida) +2:43
Points Classification
1. Elia Viviani (Quick-Step Floors) 290
2. Sam Bennett (Bora-Hansgrohe) 232
3. Davide Ballerini (Androni Giocattoli-Sidermec) 119
King of the Mountains
1. Simon Yates (Mitchelton-Scott) 91
2. Giulio Ciccone (Bardiani) 52
3. Esteban Chaves (Mitchelton-Scott) 47
NEXT UP
Yates will want to come out fighting when the riders embark on a 184km route from Venaria Reale to Bardonecchia on Friday.
