Two classic single sculls rivalries will play out on the final day of the Olympic regatta, with Tauranga's Mahe Drysdale and Emma Twigg at the heart of both.

Drysdale is on target to win a third Olympic medal and Twigg her first after both eased through semifinals on Friday (Saturday NZ Time) at Rodrigo de Freitas lagoon.

Mahe Drysdale is on target to win a third Olympic medal. Image: YouTube.

Defending champion Drysdale was particularly dominant in winning the first semifinal by three seconds. However, four-time world champion Ondrej Synek was just as impressive in clinching the second semi-final in a quicker time.

The men's single sculls final is scheduled for Saturday (1.32am Sunday NZT).

Drysdale led at every time check as the rain pelted down early in Rio, winning by 2.99 seconds from Stanislau Shcharbachenia of Belarus, with Belgium's Hannes Obreno also qualifying for the final.

Drysdale's time of 7 minutes 3.70 seconds was third-fastest in the semi-finals, with Synek and European champion Damir Martin of Croatia topping his time.

Czech sculler Synek was pipped for gold by Drysdale in London four years ago. They are expected to clear away and fight again for top spot on the dais.

Meanwhile Bay of Plenty's Valerie Adams was the top qualifier for the final of the women's shot put.

The double Olympic champion, is vying to become the first woman to win three shot put gold medals, throwing a 18.4m qualifying mark at a wet Rio Olympic Arena this morning.

The 31-year-old sent the shot out to 19.74m on her first throw to book her place in the 12-thrower final.

Tauranga sailor Peter Burling and his sailing partner Blair Tuke have made a brilliant start to their Olympic regatta taking two race wins on the opening day of the men's 49er.

Peter and Blair showed why they are favourites by using the light winds perfectly. The pair hold a six-point lead at the top of the standings, with Portugal second on eight points and the German crew in third.

Additional reporting Stuff