For the most part, the peloton and overall favourites enjoyed a leisurely day in the saddle.
"The addition of any non-essential element or device to clothing is prohibited".
The main victims became the star Spaniard Alejandro Valverde - one of the favorites of the race in turn did not keep control of the bike and at full speed crashed into the iron barrier.
Tour organisers ASO said they had deliberately avoided the hills to give sprinters the chance "to come to the fore". "No real damage, I just lost a bit of skin".
Van Avermaet had to settle for fourth at the end of the 212.5-km ride from Verviers, Belgium.
"But I don't think it's just going to be between Chris and me".
For the current edition the French authorities decided to open a wide safety device that includes the mobilization of 23 thousand gendarmes and police officers, and of effective of the forces of rapid intervention. Then he kicked his foot of the pedal.
But the sprint teams were not to be denied, catching the two leaders in the final kilometre and teeing up an outstanding sprint finish with all of the big names involved.
Thomas finished eighth, two seconds behind Sagan, to retain yellow, with team-mate Chris Froome immediately behind in ninth.
Switzerland's Stefan Kung, racing for BMC Racing, was second while Belarusian Vasil Kiriyienka finished third. In the opening week, the specialists are more likely to win stages, and that group includes the likes of Marcel Kittel, Andre Greipel, Nacer Bouhanni, Arnaud Demare and Mark Cavendish. "I said 'no, it's too much', so I relaxed a bit before going again". Thanks to 10 bonus seconds, he is now fourth in the overall ranking, losing only 13 seconds to the leader, Geraint Thomas.
The following three riders all posted the same time as Sagan with Australia's Michael Matthews of Team Sunweb finishing in second and Ireland's Daniel Martin of Quick-Step Floors in third.
Geraint Thomas became the first Welshman to lead the Tour after clocking the fastest individual time trial on a crash-filled rainy day in Duesseldorf, Germany, on Saturday.
But after the finish of the second stage from Dusseldorf to Liege, the three-time winner insisted he was fine.
"We summoned the team's sports directors to check the jerseys".
Aside from earning bragging rights, the individual who wins this year will take home €500,000.