Stomach problems took out the rest of the leading four players in Mexico, with the second seed, Casper Ruud, and third seed, Tommy Paul, both giving walkovers to their opponents, while the fourth seed, Holger Rune, withdrew trailing the American Brandon Nakashima 3-0.
Meanwhile, Alexander Zverev’s hopes of overtaking Jannik Sinner as the world No 1 were dealt a blow by a second-round loss to the teenager Learner Tien at the Mexican Open.
At the former US Open champion’s most recent tournament in Dubai last week, she was approached by a man displaying what the WTA described as “fixated behaviour” before her second-round defeat to Karolina Muchova.
Welsh has formerly worked with Leylah Fernandez, the player Raducanu beat to win the US Open in 2021, and joined the National Academy at Loughborough three years ago.
However, Zverev fell 3-6, 4-6 to the 19-year-old American Tien, who has built on his breakthrough run to the fourth round of the Australian Open last month.
