Sally Pearson could only manage seventh place on her return to action in the 100metre hurdles at the Diamond League meet in Birmingham on Sunday.
The Australian has been out since last June after suffering a dislocation and a complex fracture of both the ulna and the radius in her left arm at a meet in Rome.
Pearson had feared she might need to have her lower arm amputated, but the 2012 Olympic 100m hurdles champion finally made her comeback last weekend.
However, she finished nearly a second behind winner Kendra Harrison, who beat compatriots Brianna Rollins, Kristi Castlin and Dawn Harper-Nelson as the Americans swept the top four places.
World 200m champion Dafne Schippers was left to settle for second in the 100m as English Gardner claimed a narrow victory.
Olympic champion Kirani James triumphed in the men's 400m, while reigning world champion Asbel Kiprop emerged victorious in the 1500m with a world-lead time of three minutes and 29.33 seconds.
Conseslus Kipruto won the men's 3000m steeplechase in a race that saw the top six places taken by Kenyans.
Andre De Grasse beat Alonso Edward by one hundredth of a second in the 200m and Cassandra Tate claimed the 400m hurdles victory over Eilidh Doyle in a photo-finish.
The women's 800m went to Francine Niyonsaba and Vivian Jepkemoi Cheruiyot narrowly got the better of Mercy Cherono in the 5000m.
In the field events Buffalo Bills wide receiver Marquise Goodwin won a long jump competition in which Olympic champion Greg Rutherford could only finish fifth, Piotr Malachowski was triumphant in the discus and Mutaz Essa Barshim was first in the high jump.
Yarisley Silva set a world lead in her pole vault win and there were also victories for Madara Palameika in the javelin and Olga Rypakova in the triple jump, but two-time Olympic champion Valerie Adams was defeated by Tia Brooks in the shot put.