Serena Williams's four successive Grand Slam victories are an "incredible achievement", according to her coach Patrick Mouratoglou.
He is quoted as saying by Sky Sports News: "To win four Grand Slams in a row is an incredible achievement. Winning just one Grand Slam for anyone is such a big achievement.
"Here, she had such a tough draw, playing Heather Watson, Venus [Williams], Vika [Azarenka] and [Maria] Sharapova. The draw was so difficult, she had so many tough matches, but she made it every single time against every kind of adversity.
"She faced different gameplans, different kinds of tennis, being sick, not feeling great every day. It's incredible to be able to focus and show so much dedication and ability to turn things around when you are in trouble."
Williams's next challenge is to win all four majors in a calendar year, which she can achieve at the US Open in September.