Quick-Step Floors rider Viviani displayed his sprinting prowess at Alhaurin de la Torre to claim his first La Vuelta stage win and his 16th of the season.
Team Sky’s Michal Kwiatkowski retained the leader’s red jersey and holds a 14-second lead over Spain’s stage two winner Alejandro Valverde (Movistar), with Sunweb’s Wilco Kelderman third in the general classification.
An early breakaway led by Luis Angel Mate (Cofidis), Pierre Rolland (Education First-Drapac) and Hector Saez (Euskadi-Murias) opened up a four minute and eight seconds lead over the peloton after 34 kilometres.
But Viviani’s Quick-Step Floors team drove the main bunch and with 93km to go the gap was cut to two minutes.
Victor Campenaerts and Jelle Wallays (Lotto-Soudal), Lukas Postlberger (Bora-Hansgrohe) and Alexis Gougeard (Ag2r-La Mondiale) attacked the leading pack with 45km to go and bridged the gap further.
Jordi Simon (Burgos-BH) was unsuccessful with a couple of attacks and after Campenaerts crashed 23km from the finish, Postlberger hit the front on his own.
Austrian Postlberger held a 25 second lead with 15km to go, but was caught by the peloton with 6km left and Viviani emerged strongest in the dash for the line.
Movistar’s Valverde put a disappointing Tour de France behind him by holding off race leader Kwiatkowski in the final 50 metres of the 163.5km second stage from Marbella to Caminito del Rey.
“I had an extremely difficult Tour de France and I didn’t have all the sensations I wanted,” Valverde told Eurosport after delighting the home fans.
“So I was basically training hard to make it for La Vuelta. Thankfully our plan succeeded and I’m really happy to take this victory because I just couldn’t have done it any earlier.
“I calculated really well the distance to go and just tried to keep something back for the finish.”
An early attack saw a seven-strong group break away from the peloton but that was down to two, Alexis Gougeard (AG2R-La Mondiale) and Pierre Rolland (Education First-Drapac), with 20km to go.
The pair were gradually reeled in and Valverde showed his strength to out-sprint Kwiatkowski, with Laurens De Plus (Quick-Step Floors) finishing third, three seconds back.
Time trial winner Rohan Dennis (BMC) had a difficult day, suffering an early puncture before being dropped with 17km to go as the pace intensified.
Kwiatkowski, the Pole who finished second in Saturday’s opening time-trial, holds a 14-second advantage over Valverde heading into Monday’s 178.2km stage between Mijas and Alhaurin de la Torre.
The team will be led by Fabio Aru, who has pedigree at this race having been crowned champion in 2015.
The Italian has a long standing affection for the Spanish Grand Tour and favours the parcours in the 2018 edition.
He will be joined from August 25-September 16 by fellow countrymen Valerio Conti, Simone Consonni, Edward Ravasi and Simone Petlli, in addition to the Norwegian duo of Sven Erik Bystrom and newly crowned national road race champion, Vegard Stake Laengen.
Completing the eight person line-up will be Irishman Dan Martin, who returns to racing after a landmark Tour de France that saw him win a stage, finish eighth in the General Classification (GC) and presented with the most aggressive rider award on the Champs Elysees.
The team will be guided through Spain by three sports directors: Phillipe Mauduit, Paolo Tiralongo and Bruno Vicino.
Team Leader Aru, who will be hoping for a vast improvement having been forced to abandon his pursuit of the Giro d’Italia crown in May due to injury and illness, said: “I really like the Vuelta for many reasons: the route, the climbs and especially the fans who have always shown great affection towards me.
“I approach it with great enthusiasm and a desire to do well, also to repay the affection and support shown to me by the team, the sponsors and the fans since the Giro.
“I arrive from the first part of the season in which I did not get the results I was looking for, but from the defeats you can learn important lessons and all this gives me great motivation. It will be a tactically open Vuelta, the nine summit finishes will lend themselves to attacks.
“And I must beware of short stages, they will have a big impact on the General Classification. The competition is spread wide and level; (Miguel Angel) Lopez, the Yates brothers (Adam and Simon), (Rigoberto) Uran and the captains of Movistar… without forgetting that (Vincenzo) Nibali is also making his race return.”
Team manager Joxean Matxin added: “We will have the chance to aim for outstanding results with high-calibre and experienced riders and, at the same time, to help give some a step-up in their careers.
“Aru will be our man for the GC, in addition we will be able to count on Daniel Martin, back from an excellent Tour de France and looking for more good results in some stage finishes particularly suited to him.
“Consonni will have the opportunity to show his talent in the sprints. And Petilli and Ravasi will have the responsibility of supporting Aru and Martin the best they can on the climbs, in addition to Conti.
“I also think the contribution of the Norwegian duo Laengen and Bystrom will offer a well-rounded, robust team. Among other things, Bystrom won the 2014 world championships as an Under 23 in Spain.”
We are ready for @lavuelta 🇪🇸!— @UAE-TeamEmirates (@TeamUAEAbuDhabi) 21 August 2018
Here you got our line-up:@FabioAru1 🇮🇹@sebystrom 🇳🇴#SimoneConsonni🇮🇹@valerioconti93🇮🇹@VSLaengen🇳🇴@DanMartin86🇮🇪@SimonePetilli🇮🇹@edward_ravasi🇮🇹
📝Read the full release: https://t.co/J4ye8v0Xcq#UAETeamEmirates #LaVuelta18 pic.twitter.com/W0O5lcjQ9l
Similar to this year’s Giro, the opening stage of the Vuelta will see riders tackle a short 8km Individual Time Trial (ITT) that shouldn’t separate too many of the main GC contenders.
From there on in, it’s straight into the grit of the mountains, with Stage 2 being the first of nine summit finishes at this year’s race. Three of them are new to the Vuelta and will provide testing conditions for the riders, especially given temperatures are expected to exceed 30 degrees on most of the early stages.
Following the first rest day on September 3, riders will go up against a series of rolling hills and the longest stage of this year’s race – the 208km Stage 11 route from Provincia de Zamora to Ribeira Sacra.
The mountains come thick and fast thereafter, with three consecutive summit finishes before the second rest day on Spetember 10, followed by the second ITT on Stage 16.
Riders will be anticipating a brutal trip through the north as they make their way towards Andorra and arguably the toughest stage of the entire race – Stage 20; a summit finish at Collada de La Gallina that sees riders battle more than 1,000m of climbing for over 13km.
The final stage is set to be a procession into the Spanish capital, Madrid, where the red jersey winner will be crowned.