If he retains his title, extending his record to seven overall in the indoor hard-court event, he will match third-placed John McEnroe on the ATP's career title list with 77.
Latvala was on course for third but an electrical problem pegged him back eight minutes this morning and he ended up sixth, behind Henning Solberg in third, fourth-placed Federico Villagra and Matthew Wilson in fifth position.
The second seed took the lead for the first time in the third game of the opening set when he reached a well-placed volley by Roddick and fired a down the line winner back past his unbelieving opponent.
Alonso's quickest lap lifted him clear of second-placed Sebastien Buemi of Toro Rosso with local hero Rubens Barrichello of Brawn GP third -- as he aims for the victory that will keep his slim world title hopes alive.
He now leads Lorenzo by four points, with Rossi a further five points adrift in third, but fourth-placed Pedrosa now looks to be out of the race after another painful crash which looked to aggravate the hip injury he sustained on Saturday.