Tyson Gay sent a warning to Usain Bolt when the American clocked the fastest 100 metres time of the year, 9.77 seconds, at the Golden League series stop in Rome.
The three-time 2007 world champion Gay moved ahead of former world record holder Asafa Powell of Jamaica early in Friday's race as he equalled his personal best.
Powell clocked a season-best 9.88 seconds and compatriot Yohan Blake was third in 9.96 seconds.
Bolt, who got a golden world record treble at the Beijing Olympics, had led the 2009 list with 9.86 seconds until Friday. The Jamaican star Bolt was not competing at the Golden Gala in Rome.
The showdown between Gay and Bolt will take place at the Aug 15-23 world championships in Berlin, where Gay has 100m, 200m and 4x100m titles to defend against Bolt.
Gay is also ahead of Bolt in the year's 200m list, 19.58 seconds to Bolt's 19.59, but Bolt's time Tuesday in Switzerland came despite terrible weather conditions.
Jamaica got its revenge in the women's dash when Kerron Stewart clocked a world-leading 10.75 seconds from compatriot Olympic champion Shelly-Ann Fraser (10.91).
Stewart's victory kept her in the race for the Golden League jackpot of $1 million at the halfway mark of the six-meet series, along with Russian pole vaulter Yelena Isinbayeva, US 400m runner Sanya Richards and Ethiopian 5,000m ace Kenenisa Bekele.
The four have won in Berlin, Oslo and Rome, with the big prize going to athlete(s) who win their events in Paris, Zurich and Brussels as well.
Finnish javelin thrower Tero Pitkamaki and American 100m hurdler Damu Cherry are no longer in the frame.
Isinbayeva cleared a 2009 world best 4.85m and Bekele (a world record holder, world and Olympic champion as well) got the best 5,000m time of the year in 12:56.23 minutes.
Richards, who is gunning for a third jackpot, ran away from her rivals on the home stretch to win the 400m in 49.46 seconds. It was her 36th career race below 50 seconds, a new record as she moved ahead of world record holder Marita Koch (47.60 seconds), an East German who had 35 sub-50-second times.
Pitkamaki's jackpot hopes ended when two-time Olympic champion Andreas Thorkildsen of Norway came up with a massive final throw of 87.46m to beat the Finnish world champion who had 83.68m.
Cherry was not in the hurdles field as Olympic champion Dawn Harper of the US won the race in 12.55 seconds. In the men's 110m event, Cuban world record holder and Olympic champ Dayron Robles stretched his unbeaten 2009 run to five races with first place in 13.16 seconds.
More 2009 world leading results came from world champion Maryam Yusuf Jamal of Bahrain in the 1,500m (3:56.55) and Olympic 3,000m steeplechase gold medallist Gulnara Galkina-Samitova of Russia (9:11.58).
Dwight Philipps of the US soared a massive 8.61m for first place in the long jump. But high jump world champion Blanka Vlasic suffered her second defeat of the season, the Croatian managing only 1.97m as the Italian fans delighted in Antoinetta di Martino's 2.00m.