The Sunweb rider mathematically secured the points category for the leading sprinter during Friday's long and hot 19th stage from Embrun to Salon-de-Provence -- at 222km the longest in this year's Tour.
Matthews did not feature in the day's one intermediate sprint, which was contested by a group of 20 escapees, none of whom are remotely close to him in the points standings.
His cause was helped by the disqualification of Peter Sagan, the green jersey winner for the past five years, after stage 4 and a crash that took German sprinter Marcel Kittel, winner of five stages this year, out of the race on stage 17.
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The 26-year-old Matthews, winner of stage 14 in Rodez and the 16th stage in Romans-sur-Isere, had built up a huge 160-point lead over Germany's Andre Greipel by Friday's stage.
As long as he arrives safely in Paris, Matthews will join compatriots Robbie McEwen (2002, 2004 and 2006) and Baden Cooke (2003) in securing the green jersey.
(Reporting by Martyn Herman; Editing by Hugh Lawson)
