The revelation of last season has found her remarkable year hard to follow up, and she has still won just three matches since the Australian Open after falling to a 6-4 1-6 6-4 defeat against Kazakhstan player Yaroslava Shvedova.
Canadian Bouchard was runner-up at Wimbledon in a stellar 2014 campaign, as well as a semi-finalist at the Australian Open and French Open, climbing to number five in the world.
However a first-round Roland Garros exit has seen the 21-year-old this week fall out of the top 10, stunting the progress that at one stage looked unrelenting, with Bouchard apparently destined for the top of the game.
Shvedova had lost to Bouchard in both of their previous matches, but the 27-year-old world number 76 showed her mettle in the final set on Tuesday.
Swiss fourth seed Belinda Bencic overcame American qualifier Jessica Pegula 6-2 7-6 (7/3), but eighth-seeded Swede Johanna Larsson was a first-round victim, beaten 6-4 6-1 by Czech Klara Koukalova.
Other winners were Czech qualifier Andrea Hlavackova, Belgian Alison Van Uytvanck, Holland’s Kiki Bertens, French seventh seed Kristina Mladenovic, Russian sixth seed Anastasia Pavlyuchenkova and the German pair of Tatjana Maria and Annika Beck.
The tournament lost a major attraction in the men’s event too, as Lleyton Hewitt bowed out in the first round.
Nicolas Mahut – the man beaten by John Isner in Wimbledon’s longest ever match five years ago – claimed the scalp of the Australian.
Hewitt triumphed at this grass-court tournament in 2001, a year before he landed the Wimbledon title.
This is Hewitt’s final full season on tour, and he is on a lap of honour, but the 34-year-old wildcard could not muster the magic that brought him great success in his early twenties as he lost 6-3 6-4 to qualifier Mahut.
Seventh seed Fernando Verdasco edged past fellow Spaniard Daniel Gimeno-Traver, winning 7-6 (7/3) 6-7 (6/8) 6-2, and other winners included experienced Austrian Jurgen Melzer, Portuguese eighth seed Joao Sousa and French sixth seed Adrian Mannarino.
Qualifiers Tatsuma Ito and Marco Chiudinelli also advanced, the Japanese in straight sets against Lithuanian Ricardas Berankis and the Italian with a 7-6 (7/3) 2-6 7-6 (7/4) success against France’s Benoit Paire.
Russian Mikhail Youzhny, who has played well on grass in the past, lost 6-4 6-4 to Ukrainian qualifier Illya Marchenko.