Bernard Tomic took over from Lleyton Hewitt, who succeeded Pat Rafter as Australia's top-ranked male tennis player.
On Monday, the No. 1 baton will pass to Marinko Matosevic, the 27-year-old Victorian who was overlooked for attitudinal reasons for the Davis Cup playoff in September and is yet to win a grand slam match.
Having beaten seventh seed Florian Mayer 6-2, 6-3 in the first round of the Swiss Indoors in Basel yesterday, Matosevic is assured of breaking into the top 50 for the first time, at No. 47 or higher, while Tomic will drop one rung to 49th after his latest opening round loss - a 6-0, 6-2 thrashing from Mikhail Youzhny at the same tournament.
Bosnian-born Matosevic started the year ranked outside the top 200, but the volatile right-hander with the world-class backhand has risen steadily for much of a season in which he reached his first ATP final (losing to South African Kevin Anderson at Delray Beach), and five quarter-finals, has won 17 of his 35 matches and was still combining tour events with some Challenger level tournaments as recently as June. In Basel, he will play Anderson for a place in the last eight.
Tomic, meanwhile, may have been spared the decision on whether to contest a final tournament for 2012, having failed to earn direct main draw entry to next week's Paris Masters, although whether the 20-year-old intends to contest the qualifying event is unknown.
Renowned coach Darren Cahill is among those to have urged Tomic to end his season and concentrate on preparing for 2013. He has not beaten a player ranked above him since January.