Sydney FC are nearing their battle-hardened best as the business end of the A-League approaches, coach Graham Arnold believes.

The Sky Blues extended their season-long streak without a loss away from home with an emphatic 3-0 win over a depleted Wellington Phoenix on Sunday.

Former Phoenix striker Shane Smeltz celebrated his return to Wellington with a goal and an assist as Sydney fired home three first-half goals to all but wrap up the win before the break.

Jacques Faty's seventh minute goal from a Smeltz nod-down kickstarted proceedings, with Smeltz doubling the lead 20 minutes later.

A goalmouth scramble five minutes before half-time left Wellington keeper Glen Moss flat-footed as the ball trickled over the line from a Phoenix touch for an own goal. With only four matches left in the regular season and an unbeaten record away from home, Sydney will be nearing their peak at the right time, Arnold said.

They host Adelaide United next week, then travel to Perth to meet the Glory before returning to Wellington in the last game of the regular season.

"What I will say is at the end of these four weeks, because we've got tough games, we're going to be match-hardened for the finals series.

"If we get through that, and if we get through that well, then we'll be match-hardened, much harder than some of the other teams with their run-ins."

Both teams finished Sunday's match with 10 men; Phoenix midfielder Albert Reira was sent off after receiving a second yellow card for fouling Milos Dimitrijevic in the 67th minute and Smeltz was shown a straight red two minutes later after kicking out at Ben Sigmund.

Wellington still sit atop the league ladder, but now only have a one-point margin over Melbourne Victory, Sydney and Perth Glory.

Coach Ernie Merrick said there was no doubt missing six players to the international window had a significant impact on his team, with the absence of striker Nathan Burns and playmaking midfielder Michael McGlinchey particularly heavy.

"We really couldn't get our midfield game going - the stats showed we had more passes than them, but it wasn't in the front half," he said. - AAP