Australian Matt Denny has capped his career-best season with a second straight Diamond League final discus victory in Brussels and gone within a whisker of smashing the 70m barrier for the first time. 

The Paris Olympics bronze medallist broke the Australian record for the second time this year with a huge opening-round throw of 69.96m and was never headed.

"I thought that 70m was on the cards tonight but you never know with changing conditions," said the 28-year-old Queenslander, who also broke the 40-year-old meet record.

"First round was a nice one to win it, but what I've learnt winning last year and this year is that I'd rather do it in the last round than the first round.

"It's a lot more stressful to do it in the first round when you're waiting for guys like (world record holder) Mykolas (Alekna) and Daniel (Stahl) and Kristian (Ceh) to finish out their comp and you don't know if you've got it or not."

Denny broke his previous national record of 69.35m set at the Australian championships in Adelaide in April.

Alekna was second in Brussels with 68.86m.

"It's about when we get to 70m now," said Denny.

"I thought there was a 71m throw in me tonight if I'm honest.

"We've got a big focus for the beginning of next year.

"I'm going to go to the US and chase that world record and I know a lot of the other guys here tonight will be there too."

The other stand-out Australian performance on the opening night of the Diamond League final came from two-time Olympic high jump medallist Nicola Olyslagers, who finished second on countback behind Ukrainian world record holder Yaroslava Mahuchikh.

Both jumpers cleared 1.97m, but the Australian was nudged out of first place after needing two attempts at 1.95m and 1.97m.

It was a third straight Diamond League final win for Paris Games gold medallist Mahuchikh.

Olympic bronze medallist and 2022 world champion Eleanor Patterson was fourth.

Norwegian world number one Jakob Ingbrigtsen won the men's 1500m in a photo finish in three minutes 30.07 seconds and peerless Swedish pole vaulter Armand Duplantis claimed yet another victory with a best clearance of 6.11m.

The 100m crowns went to Olympic champ Julien Alfred from St Lucia (10.88) and Jamaican Ackeem Blake (9.93).

Olympic pole vault champion Nina Kennedy is among four Australians in action on the concluding second night of the Diamond League final in the Belgian capital on Saturday (early Sunday AEST).

She will be joined by Paris Games silver medallist Jessica Hull and Georgia Griffith in the women's 1500m and Mackenzie Little in the javelin.

AAP