Thomas Barr blazed into the semi-finals of the 400m hurdles at the Tokyo Games, finishing second in his heat behind world-record holder Karsten Warholm.

Handed a favourable draw alongside Warholm, who was in lane 8, Barr had the perfect chance to test himself against the best and was not found lacking.

The Waterford man was always expected to progress to the semi-finals and did so with the minimum of fuss.

Warholm set a blistering pace from the start but Barr, who finished fourth in Rio, was able to keep the gap between the two close.

There was a slight moment of concern on the home turn when Barr winced and appeared to struggle slightly for a moment but he dug deep to overtake Italy's Alessandro Sibilio and finished very strongly to finish second in 49.02, with Warholm winning in 48.65.

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Barr was the 11th fastest of the 23 qualifiers and will go in the second semi-final at 11.15am Irish time on Sunday.

He runs in lane 4 and will again line up beside Warholm, as well as American medal prospect Benjamin Rai.

"Job done," the 28-year-old told RTÉ Sport afterwards. "Today was about coming out and getting myself into the semi-final.

"I'm always nervous for the first round, because I don't know where I'm at or how it's going to go. But I'm nicely confident after that. I felt very in control for the first 250/300 (metres).

"I probably dropped a little bit of of concentration in the top end but I knew I had enough in reserve to come down the home straight strong.

"I was aiming for second place. Warholm could have turned on the taps if I went past him. He told me beforehand he was going to take it easy so I thought I'd just hold onto him as long as I can.

"I managed to do that and held off the German (Luke Campbell) for second."

"Coming into hurdle eight I stuttered quite badly because I was coming into it on 14 strides and was very close to it, which is not usually like me. But I executed the strike pattern I wanted and got the job done."