Olympic champion Jason Kenny faces a battle to progress in the men's sprint on day four of the Track Cycling World Championships in Cali, Colombia.
The 25-year-old from Bolton faces fastest qualifier Francois Pervis of France - winner of the Keirin on day two and one-kilometre time-trial on day three - in the best-of-three quarter-finals after making slow progress through the early rounds.
Kenny advanced to the last eight by the width of a tyre after falling into the second round repechage, having been beaten by Germany's Stefan Botticher in the second round.
Robert Forstemann of Germany, the third-fastest qualifier, took the initiative in the three-man race by riding quickly from the off, leaving Kenny, the 14th-fastest qualifier, to chase along with his fellow Briton Matt Crampton.
Kenny narrowly overhauled the German on the line, the result determined by a photo finish that barely looked decisive, leaving Forstemann eliminated alongside Crampton.
Pervis stands between Kenny and a place in Sunday's semi-finals.
Olympic champion Laura Trott, Kenny's girlfriend, was second behind defending champion Sarah Hammer of the United States after two of six disciplines in the women's omnium.
Trott, the 2012 world champion and silver medallist 12 months ago, was third in the flying lap, before an excellent performance in the points race, long acknowledged as her Achilles heel in cycling's equivalent of the heptathlon.
Hammer recovered from a puncture to claim a lap and win the points race, but Trott showed great maturity to accumulate points in the sprints, including one in the final dash to the line which saw her secure third place in the discipline.