Australia's Lakeisha Patterson has won gold at the Rio Paralympics in the S8 400 metres freestyle in world record time.

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Patterson led from the 100m mark to defeat the former world record holder, Jessica Long of United States.

Nicknamed 'Lucky', Patterson sliced 0.11 of a second off the previous world mark held by Long to win in 4 minutes and 40.33 seconds, with the American touching the wall in 4:47.82.

Patterson's fellow Australian Maddison Elliott was fourth in a time of 5.02.13.

"It was pretty surreal really," Patterson told APC Media.

"I knew I had to attack and go out hard and keep fighting for it, and I knew she was right behind me, so I just had to keep going forward.

"Jess is an amazing and fierce competitor, and to be able to race alongside her and get past her was bitter sweet because she has been my idol growing up. So to race alongside her, and end up on top is quite amazing.

"Jess said she was really proud of me and can't believe how well I've done, and I really appreciated that, it was really nice. To hear those nice words from her really made me feel special."

Patterson will next swim the heats of the women's 100m butterfly, the second of six individual events she is contesting in Rio.

Powell wins first Rio medal

Earlier, Sue Powell claimed Australia's first medal of the Games by taking silver in individual pursuit cycling.

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The 49-year-old was beaten for gold by the reigning world champion Shawn Morelli from the US.

The silver medal is Powell's third Paralympic medal since suffering a spinal cord injury that affects her right leg.

"I've work my arse off the last few years to try to just get that one more great time," Powell said.

"I think this morning I put down a really good ride, which I'm proud of. I didn't quite back it up tonight but I'm still really stoked."

Australia won two bronze medals in the track and field program, with Carlee Beattie (F47 long jump) and Angie Ballard (T53 100m) managing podium finishes.

Meanwhile, Melissa Tapper, who last month became the first Australian athlete to compete at both the Olympic and Paralympic Games in the same year, began her 2016 table tennis campaign in Rio with a triumph.

Tapper won her opening match in the classification 10 competition against Turkey's Umran Ertis 3-1 (11-2, 11-4, 10-12, 11-9).

"It's so good to get that first win under my belt this early on," Tapper said.

"I started off very strong but it was expected that she would come back into it and find a bit of a groove.

"It was quite a battle in the end, but it was great to have that fight in the first match because it will prep me well for my later ones."

Smith manages top-eight finish in shooting

Natalie Smith finished fifth in the women's 10-metre air rifle standing SH1.

"We all want to win gold, but I'm really pleased with fifth," Smith said.

"The competition coming into this has been very tough. I knew I really had to perform and I just dropped a couple of shots there but it just took me out."

Smith will next compete in the mixed 10m air rifle prone SH1 on the weekend.

Her countrywoman Libby Kosmala was 18th in qualifying for the women's 10m air rifle standing SH1 and did not progress to the final.

The 74-year-old Kosmala, a nine-time Paralympic gold medallist, is competing at her 12th Games.