For the first time in the Open Era, the top two seeds in the men’s and women’s draws have been knocked out of a Grand Slam before the quarter-finals.In the men’s draw, top seed Rafael Nadal and second seed Casper Ruud both lost their second-round matches, while in the women’s draw, top seed Iga Swiatek was knocked out in the fourth-round and second seed Ons Jabeur fell in the second.There has been much speculation over the cause of so many upsets, but Eurosport expert and former world number two Alex Corretja believes there are four main reasons, including the balls, which explains why so many seeds have been knocked out before …