Keely Hodgkinson safely through as she celebrates birthday in style in Istanbul
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Hodgkinson, who turned 21 on Friday, won her heat at the Atakoy Athletics Arena in a time of two minutes and 1.67 seconds ahead of Germany's Majtie Kolberg.
"It was okay. I felt like I was front-running around, you don't want to make any mistakes ," said Hodgkinson, who set a new British record when winning the World Indoor Tour in Birmingham last week.
"You are happy to qualify and that it was not a messy race, so you are clean through.
"Sometimes running at that pace is harder than what you are used to, I am actually quite tired.
"But I am sure I will be okay by Saturday then come back on Sunday to get the job done."
Hodgkinson was runner-up at the World Championships in Eugene last year and also won Olympic silver in Tokyo as well as the 2022 European outdoor title.
"I will spend my birthday recovering (on Friday)," she told BBC Sport. "It will be a nice present to myself if I can (then) defend my title.
"Just to be able to share the moment with the people who worked so hard for me to be here, I am looking forward to it and hopefully making everybody proud."
Isabelle Boffey also won her heat in 2min 3.24sec to progress.
The Enfield & Haringey athlete said: "It is always a bit weird going on a new track, so I am definitely happy to have got the win now and to have secured the auto-qualification for the semi-final.
"I am learning how to do the big races and have got a lot better at that this year, so it is just sort of repeating what I have done this season."
Neil Gourley and George Mills qualified for the men's 1500m final, while Melissa Courtney-Bryant and Hannah Nuttall both reached the 3,000m final.
Gourley, who clocked the fastest time of 3:41.08, said: "The idea was to get through as smoothly as possible.
"I contributed a bit, to keep it moving and stay out in front a little bit, so I am happy with the way I handled it.”