Raducanu losing to Sierra was not a surprise in itself, even though the Briton is ranked 29 places higher in the world.
Since Indian Wells in early March, Raducanu has only played one match – and that only came last week in a straight-set defeat by France’s Diane Parry in Strasbourg.
The post-viral issues have continued to have lingering effects and she was struggling with a cough in Paris.
A healthy Sierra, on other hand, has plenty of matches in her legs and more rhythm in her racquet.
The difference was clear in a woeful first set from Raducanu.
The 23-year-old’s tactic of aggressively hitting early in the rallies, and a reluctance to patiently wait for chances to attack, underlined her keenness to swarm her opponent.
Her lack of court time, plus the 30C heat in Paris, meant it made sense for Raducanu to try to end the points quickly.
However, her timing was well out and led to a high volume of unforced errors.
“I felt like the conditions were extremely lively, and I felt like I wasn’t able to kind of trust my shots in that and didn’t feel like I had control over the ball,” Raducanu said.
“It was a really difficult set-up for me to step into, having not had many matches.
“I think probably just a bit light on matches, a bit light on confidence coming into the tournament.”
Sierra was always going to provide a tricky test, especially at this early stage of Raducanu’s latest comeback.
Having started playing on the red dirt aged three, 21-year-old Sierra demonstrated her ability by recently pushing reigning French Open champion Coco Gauff in Rome.
