Summer McIntosh‘s pursuit to win five solo gold medals at the swimming world championships this week remains on track after the Canadian sensation withstood a plucky challenge from American Alex Walsh to grab her second title on Monday night.

McIntosh, 18, triumphed in the 200-metre individual medley on night two in Singapore to ensure her bid to become only the second swimmer to win five individual gold medals at a single long-course world championships remained intact.

After hitting the halfway mark leading Walsh by a full body length — to be precise, 1.36 seconds — McIntosh turned for the final time with an advantage of only 0.33 of a second.

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Walsh had produced a powerful breaststroke leg in which she split 37.03 seconds — considerably quicker than the 38.06 recorded by McIntosh.

“We weren’t expecting this,” said Nine caller Mat Thompson.

“We thought Summer would come out and blow the field away. Can Alex Walsh cause a massive upset here?”

Watch the World Aquatics Championships live and free on Nine and 9Now.

Australian swimming legend Ian Thorpe added: “They’re both on fire here. Summer McIntosh has got a challenger.”

But McIntosh motored through the freestyle leg in 30.16 seconds to reach the wall well before her US rival, who split 31.72.

“She was under threat with 50 [metres] to go but she has blown Alex Walsh away, and Summer is shining brightly in Singapore,” Thompson said.

McIntosh won gold with a time of two minutes, 6.69 seconds (2:06.69), with Walsh picking up silver in 2:08.58 and Canadian teammate Mary-Sophie Harvey collecting bronze in 2:09.15.

At just 12 years of age, Chinese prodigy Zidi Yu took fourth and finished only 0.06 of a second off the podium.

McIntosh is 18, Walsh is 23 and Harvey 25.

The greatest male swimmer of all time, US legend Michael Phelps, is the only athlete who’s won five individual gold medals at a single long-course world championships — a feat he achieved in Melbourne in 2007.

Having won gold in the 400m freestyle on Sunday night and another gold in the 200m individual medley on Monday night, McIntosh must now triumph in the 200m butterfly, 800m freestyle and 400m IM to complete the feat.

The three-time Olympic gold medallist will have to defeat the greatest female swimmer of all time, American icon Katie Ledecky, and in the US legend’s pet event no less: the 800m freestyle.

Ledecky has won the past four Olympic 800m titles and is eyeing off her seventh world championship gold medal in the 16-lap event.

The only woman who’s beaten Ledecky in an 800m final since 2010 is McIntosh, who did so at the age of 17 in February last year.

“My goal was to get my hand on the wall first, so to get that done is good,” McIntosh said after her win on Monday night.

“I’m not super happy with the time, but honestly, at a world championships, my goal is just to go as fast as I can against my competitors.

“Still happy with the gold and hoping to keep up my streak next time.”

Night two of the world championships also saw Australia’s Alexandria Perkins pick up bronze in the 100m butterfly.

In doing so, the Sunshine Coast swimmer won her maiden individual medal at a global championship.

US swimmer Gretchen Walsh, the younger sister of Alex Walsh, captured gold in 54.73 seconds, ahead of Belgium’s Roos Vanotterdijk (55.84) and Perkins (56.33).

“I couldn’t be happy, honestly,” Perkins said.

“I tried not to expect anything going into that final. I just wanted to put my best foot forward and be proud of what I’ve done.

“Coming away with the medal is just a bonus.”