Emma Raducanu laid down a marker for her Wimbledon rivals after thrashing Elise Mertens 6-1 6-2 to reach the third round. The 2021 US Open champion has been close to her best since the start of the grasscourt season and had strong runs in Nottingham and Eastbourne heading into Wimbledon. A first-ever win against a top-10 opponent last week in Jessica Pegula filled Raducanu with plenty of confidence. But her first-round match was far from convincing, despite playing against someone making their main draw debut at Wimbledon. Renata Zarazua caused Raducanu all sorts of problems, but Raducanu show…