Belgium's Wout van Aert beat defending champion Julian Alaphilippe in a thrilling sprint finish to win his first Milan-San Remo title in Italy.
Frenchman Alaphilippe attacked to lead the race solo over the final climb with 5.5km to go but Van Aert reeled him in on the descent.
They held off the chasers into San Remo, with Alaphilippe kicking for the line first, but Van Aert powered home.
Elsewhere, Chris Froome again struggled and lost time at the Tour de l'Ain.
And Belgium's Remco Evenepoel dedicated his solo victory on stage four of the Tour of Poland to Deceuninck-Quick-Step team-mate Fabio Jakobsen.
It is a second win in as many weeks for Jumbo-Visma rider Van Aert, 25, following victory in Strade-Bianche, the first World Tour race held after the season was delayed by the coronavius pandemic.
This is his first victory in a 'monument' classic - cycling's five oldest and most prestigious one-day races.
"I'm super happy - I can't believe I've taken these these two victories in a row," said Van Aert.
"I don't have words actually - I know everyone says that when they win a monument but to start the second part of the season like this, it's crazy."
The race was scheduled to be held on 21 March but was postponed because of the pandemic, with the 305km route also changed to run more inland after coastal towns opted against closing their roads in favour of keeping them open for tourists.
The course did still contain the traditional final two climbs of the Cipressa and the Poggio, with Bora-Hansgrohe's Daniel Oss going clear on the former before he was caught.
Gianluca Brambilla and Aime de Gendt then attacked on the Poggio, with the latter briefly going solo, before Deceuninck-Quick-Step's Alaphilippe and then Van Aert came past to contest the finish, with Australia's Michael Matthews claiming third.
Froome falters again
Slovenia's Primoz Roglic held off Tour de France champion Egan Bernal by 12 seconds to win stage two of the Tour de l'Ain and take the leader's jersey.
Bernal's Ineos team-mates Geraint Thomas and Froome both lost time, with the Welshman finishing over four minutes back on Roglic and Froome particularly struggling, losing 12 minutes in France.
Froome, who will join Israel Start-Up Nation at the end of the season, finished nearly 10 minutes behind race winner Bernal at last week's Route d'Occitanie.
Britain's four-time Tour winner Froome, 35, risks not being selected for this year's race, which starts on 29 August, if his form is not deemed strong enough.
The third and final stage of the Tour de l'Ain takes place on Sunday.
In Poland, 20-year-old Evenepoel attacked with 51km to go and stayed clear to the line, holding up the bib number 75 of Dutchman Jakobsen as he crossed the line.
Jakobsen, who had facial surgery after a high-speed crash on stage one of the race, is now out of a coma and in a good condition, but is expected to face a long recovery.
Milan San-Remo top 10
1. Wout van Aert (Bel/Team Jumbo-Visma) 7hours 16mins 09secs
2. Julian Alaphilippe (Fra/Deceuninck-QuickStep) Same time
3 Michael Matthews (Aus/Team Sunweb) +2secs
4. Peter Sagan (Svk/Bora-Hansgrohe) Same time
5. Giacomo Nizzolo (Ita/NTT Pro Cycling)
6. Dion Smith (NZ/Mitchelton-Scott)
7. Alex Aranburu (Spa/Astana Pro Team)
8. Greg van Avermaet (Bel/CCC Team)
9. Philippe Gilbert (Bel/Lotto-Soudal)
10. Matej Mohoric (Slo/Bahrain-McLaren)