After smashing the second-oldest track world record yesterday at the Rio Games, new Olympic 400m champion Wayde van Niekerk said he had expected a hamstring niggle to hit him in his historic final. Van Niekerk was sensational as he destroyed a field starring 2012 Olympic champion Kirani James and 2008 titleholder LaShawn Merritt, despite running unsighted in the outside lane.He crossed the line first in 43.03sec to bag South Africa's first gold of Rio 2016 and push the medal tally to seven, the country's highest number since readmission in 1992.Michael Johnson's 43.18 mark from 1999 is finally history; Van Niekerk is the trailblazer now.He is SA's first Olympic track champion since 110m hurdler Sid Atkinson in 1928, and the first Games sprint champion since Bevil Rudd won the 400m in 1920.Van Niekerk is also SA's first reigning world champion to add the Olympic crown in the same event, a feat swimmer Chad le Clos was unable to accomplish in the 100m butterfly on Friday night.He also has the pleasure of winning an Olympic medal alongside cousin Cheslin Kolbe, bronze winner with the Blitzboks.Van Niekerk admitted afterwards he had struggled with a hamstring niggle in the heats and semifinals, during which he had appeared stiff."Those were mentally very challenging. In the heats and the semifinal, I felt a bit of a niggle in my hamstring as I hit the 200m."Van Niekerk suffered recurring hamstring injuries early on when still running the 100m and 200m.But those eased off after coach Ans Botha moved him to the 400m, which needs less explosive power."When I got to the final I hit the 200m expecting the feeling again but I felt nothing and I was like, 'Okay, don't lose this opportunity,' and I tried to push."And push he did, crossing the line with a massive gap between himself and James, second in 43.76, and Merritt, third in 43.85."I did think he was going to fade a little bit, I honestly did, but he was so far out," said Merritt.Said James: "I tried to go with him from 200m and he just kept going and never slowed down."When you do something like that, obviously a world record's going to happen."Kolbe revealed yesterday that Van Niekerk had predicted his superb run. The pair spent time together in the Olympic Village but Kolbe didn't see the race live because he was flying back from Rio."Wayde was confident going into the race and to see someone crank up his speed in a race of that magnitude was phenomenal."He even predicted he would run a 42-second race and he's not far off that now. In his next race he will break 43 seconds," Kolbe said minutes after landing. -Additional reporting by TMG Digital..