The Neptune swimmer touched the wall in 8min28.72sec in a big personal best, lowering the time of 8min29.3sec she set at the national championships earlier this year.
Deans finished 10th overall in the 800m discipline after being drawn in a stacked heat against United States great Katie Ledecky, Australian Lani Pallister and German Isabel Gose, who are in the top four seeds for the final.
Former Dunedin swimmer Erika Fairweather, also in the same heat as Deans, qualified sixth for tonight’s final in 8min22.22sec.
Earlier in the week, Deans, who represented New Zealand at the Paris Olympics, finished 13th in the women’s 1500m freestyle in 16min13.16sec.
Kiwis Zoe Pedersen and Laura Quilter, returning internationally for the first time since 2014, finished 24th and 29th respectively in the women’s 50m butterfly.
Clareburt collected his second personal best of the championships when he touched the wall in 1min57.06sec, lowering the previous record of 1min57.27sec from the Tokyo Olympics.
French swimmer Leon Marchand, who set a world record in the distance during the semifinals, won gold in 1min53.68sec.
Shaine Casas, of the United States, was second and Hungary’s Hubert Cos won bronze.
Quilter is back in the pool in the women’s 50m freestyle heats and Andrew Jeffcoat and Finn Harland are in the men’s 50m backstroke heats today.
Fairweather will race in her final tonight and Clareburt will be out to defend his title in the men’s 400m IM tomorrow.
