Watkins Glen IndyCar: Scott Dixon tops third practice for Ganassi

Ryan Hunter-Reay completed the top three, with Helio Castroneves in fourth.

Dixon, who also topped second practice on Friday, waited until late-on in the 45-minute session to show his true pace, as his best time of 1m22.644s came with just five minutes remaining.

Rossi's fastest lap was just 0.022s slower than Dixon, with his Andretti Autosport team-mate Hunter-Reay a further 0.393s back.

Castroneves ended up as the fastest of the Chevrolet-powered runners, albeit over half a second behind Dixon's best effort.

Sebastien Bourdais, who is returning to action at a road course race for the first time since his violent crash at the Indianapolis 500 in May, rounded out the top five despite spinning on his final lap.

Takuma Sato finished in sixth fastest, ahead of first practice pacesetter Graham Rahal.

Championship leader Josef Newgarden could only manage eighth fastest, as he had visible issues with understeer and traction over the course of the session.

Newgarden's Penske team-mate Simon Pagenaud was eighth, and Charlie Kimball rounded out the top 10.

Several star drivers ended up well down the field - Tony Kanaan was 12th, while Will Power and James Hinchcliffe could only manage the 16th and 17th fastest times.