Mitchelton-Scott took victory in dangerous conditions during the opening team time trial of the 2019 Tirreno-Adriatico, with Adam Yates best placed out of the general classification riders.
The Australian squad surprised other teams traditionally strong in the discipline, including Jumbo-Visma who looked sure to win the opening stage.
Australian Michael Hepburn takes the leader's jersey heading into stage two.
Primož Roglič, riding high from overall victory in the Middle East stage race, is the next best place general classification contender with a seven second deficit.
Tom Dumoulin's Sunweb squad are third on GC with a 15- second deficit.
Geraint Thomas and Wout Poels for Team Sky are 40 seconds back from the leader.
The opening 21.5km team test took in the familiar seafront roads of Lido di Camaiore over a pan-flat flan course.
Riders faced a cluster of sharp turns before turning back on themselves to race back along the same route to the finish.
The rain-soaked roads made for tense racing early on, but it was a crash with a pedestrian that caused havoc for Bora-Hansgrohe.
Oscar Gatto and Rafał Majka collided heavily with a man who had walked onto the course, leaving Bora to finish with five men.
Both Gatto and Majka were able to get back on their bikes and finish the course, although at a major deficit.
The turned in the as the afternoon wore on and the roads quickly dried, benefitting the teams that started their rides later.
EF Education First set the early benchmark with a time of 23-21, but were bested by TTT world champions Deceuninck – Quick-Step who went 19 seconds faster.
Jumbo-Visma were able to benefit from the drying conditions to go 30 seconds faster than Quick-Step, with Tom Dumoulin's Sunweb squad the only real threat left to race.
But the heavens opened once again, leaving Sunweb to race in damp conditions.
The strong performance from the German team wasn't enough to put Dumoulin into the lead, as they finished 15 seconds down to Jumbo-Visma.
But it was the Australian Mitchelton-Scott ream, led by Adam Yates, who defied the expectations to knock Jumbo-Visma out of the hotseat, finishing seven seconds faster.
Tirreno-Adriatico 2019, stage one: Lido di Camaiore to Lido di Camaiore (21.5km TTT)
1 Mitchelton-Scott (Aus), in 22-25
2 Team Jumbo-Visma (Ned), at 7s
3 Team Sunweb (Ger), at 22s
4 Deceuninck-Quick-Step (Bel), at 37s
5 Team Sky (GBr), at 47s
6 Lotto-Soudal (Bel), at 54s
7 EF Education First (USA), at 56s
8 Groupama-FDJ (Fra), at 58s
9 Israel Cycling Academy (Isr), at 1-05
10 Bahrain-Merida (Brn), at 1-10
11 CCC Team (Pol), at 1-12
12 Trek-Segafredo (USA), at same time
13 Astana Pro Team (Kaz), at 1-13
14 UAE Team Emirates (UAE), at 1-19
15 Movistar Team (Esp), at 1-32
16 Dimension Data (RSA), at 1-34
17 Katusha-Alpecin (Sui), at 1-38
18 Gazprom-Rusvelo (Rus), at 1-40
19 Cofidis, Solutions Credits (Fra), at 1-54
20 Bora-Hansgrohe (Ger), at 1-57
21 AG2R La Mondiale (Fra), at 2-01
22 Neri Sottoli Selle Italia KTM NSK (Ita), at 2-10
23 Bardiani CSF (Ita), at 2-41
General Classification after stage one
1 Michael Hepburn (Aus) Mitchelton-Scott, in 22-25
2 Brent Bookwalter (USA) Mitchelton-Scott
3 Luke Durbridge (Aus) Mitchelton-Scott
4 Adam Yates (GBr) Mitchelton-Scott, all at same time
5 Alexander Edmondson (Aus) Mitchelton-Scott, at 3 seconds
6 Jos van Emden (Ned) Jumbo-Visma
7 Primož Roglič (Slo) Jumbo-Visma, at 7 secs
8 Koen Bouwman (Ned) Jumbo-Visma
9 Tony Martin (Ger) Jumbo-Visma
10 Laurens De Plus (Bel) Jumbo-Visma, all at same time
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