Sydney FC coach Frank Farina concedes his side's recent knack of picking up red cards on the road is "killing" them.Sydney haven't won away from home since their 2-1 win over Wellington on December 9, with the Sky Blues losing five and drawing two since then.But it is their past four away games that has caused particular concern to Farina, who has watched his team pick up five red cards in that time.Fabio Alves has been sent off twice during that period, with the latest a 56th-minute red card in Saturday night's 2-1 loss to Perth.With just four rounds remaining, eighth-placed Sydney have plenty of work to do if they are to make the finals.Farina said his star-studded team needed to clean up their discipline in order to be a more competitive force on the road."People ask me the question, 'why is it you haven't won away from home in the last six games'," Farina said."There's a very simple answer to that - you've got to try to keep 11 men on the park if you're going to have a chance, and we haven't done that."It's killing us. It's making it really hard for the rest of the players that do stay on."Luckily for Sydney, their next two games are at home.Unfortunately though, those games are against Central Coast and Melbourne Victory - two teams right in the mix to win the championship.And it doesn't get any easier after that, with Sydney rounding out the season with away games against the high-flying Western Sydney and defending premiers Brisbane.Farina has labelled Saturday night's clash with the Mariners at Allianz Stadium a "must-win".But Sydney will be sweating on the fitness of Socceroos skipper Lucas Neill, who pulled up tight in his calf after the Glory game.Italian great Alessandro Del Piero scored his 12th goal of the season with a stunning 27-metre thunderbolt against the Glory.But first-half goals to Chris Harold and Shane Smeltz were enough to lift Perth to their second win from three games under new coach Alistair Edwards.Edwards was pleased with the performance of midfielder Daniel De Silva, who turns 16 next Wednesday and became the second youngest debutant in A-League history when he came on as a 62nd-minute substitute.The interim Glory coach also hinted the club would announce the signing of a couple more up-and-coming players over the next fortnight.Perth defender Steve Pantelidis is in doubt for Friday night's encounter against Newcastle at Hunter Stadium after injuring his Achilles tendon.