Carina Horn finally broke Evette de Klerk’s 28-year-old 100m South African record at the national championships in Pretoria on Thursday.

Horn, 29, clocked 11.03sec — improving on the 11.06 mark she had shared with De Klerk since mid-2015 — as she won her semifinal to set herself up as favourite for the women’s final on Friday night.

In the men’s sprint two old-timers were the quickest in the semifinals after favourite Akani Simbine pulled out as a precaution.

Simbine, fifth at the 2016 Rio Olympics and 2017 world championships, felt discomfort in his hamstring and decided not to risk injury — as happened to him at the national showpiece two years ago.

Fans might miss Simbine’s speed in the final — he was, as expected, the quickest of the heats — but with the top four semifinal finishers separated by only five-hundredths of a second, they could be treated to a nail-biter.

Roscoe Engel, 29, was the fastest of the semifinals as he clocked a 10.06sec career best to take pole position ahead of former six-times champion Simon Magakwe, 32, the second-fastest overall in 10.09.

Magakwe, the first South African to break 10 seconds in the 100m in 2014, was banned for two years in early 2015 after refusing to take a dope test.

Last year he made only the semifinals at the national championships and on Thursday he produced the fourth-best time of his career.

Magakwe, who ran his 9.98 at the same Tuks stadium before it was revamped with the Mondo surface, won his semifinal ahead of 200m star Anaso Jobodwana, second in 10.21.

Henricho Bruintjies, the 2016 SA champion, won the third semifinal in 10.10. Young Thando Dlodlo went 1/100th of a second off the SA junior record — as he finished second behind Engel.

Jobodwana, who is finally returning to form after a lengthy battle with injury, also cannot be discounted as a contender in the final.

The big guns of the men’s 400m hurdles all qualified for Saturday’s final.

Lindsey Hanekom was the quickest in 49.39, while Cornel Fredericks (49.79) and Constant Pretorius (49.96) also broke 50 seconds.

They will go up against veteran LJ van Zyl, reigning champ LeRoux Hamman and world under-18 king Soks Zazini.

But defending champion Dumisani Hlaselo was the big casualty in the men’s 1500m, failing to progress beyond the heats that were dominated by Jerry Motsau and Treasure Derison.

Wenda Nel will be the overwhelming favourite in the women’s 400m hurdles.

Phil-Mar Janse van Rensburg won the men’s javelin title in 76.65, while Rocco van Rooyen, who has a few 80m-plus throws under his belt, was fourth in 72.71.

Julia du Plessis won the women’s high jump with an effort of 1.80m and Margo Coetzee the women’s hammer (58.97m).