Some would use it as a stick to beat them with but Sydney FC's stingy defence and impressive team structure should be revered rather than reviled.

The pre-match narrative for City versus Sydney on Friday night had been that if the Westfield FFA Cup winners could hand the Hyundai A-League leaders a second straight loss, Victory could have moved within five points of the Sky Blues ahead of next week's Big Blue.

Instead, Sydney notched their 15th win of the campaign in a match that underlined why Arnold's men are almost certain to lift the Premiership and are favourites for the Championship.

Bobo brace fires Sydney FC past 10-man City

The Sky Blues are the only team in the A-League that can defend properly.

The competition-wide obsession with playing attacking football may tick the box from an entertainment sense but if Australian football is to take the next step, A-League clubs must get better at defending and controlling games.

Sydney have conceded just 11 goals in 21 matches this season at an average of just over half a goal per game in 2016/17.

Every other team is letting in goals at an average of more than one per match.

Sydney didn't produce their best performance against City but the contest turned on Manny Muscat's first-half red card, which halted the hosts' momentum and highlighted the kind of defensive errors that occur too often in the A-League.

The visitors opened the scoring in the 24th minute after Muscat fouled Filip Holosko in the penalty area.

City defender Osama Malik failed to clear the ball earlier in the attack and Holosko burst into the box only to be felled from behind by Muscat, allowing Bobo to convert from the spot.

The home side were almost immediately on level terms as Nick Fitzgerald struck an amazing half-volley with the outside of his right boot but six minutes before the break Muscat was off, ruining City's chances of victory.

Muscat was caught on the ball by Alex Brosque, who claimed possession and surged towards goal only to have his shirt tugged by the 32-year-old former Wellington Phoenix defender, prompting referee Jarred Gillett to brandish a second yellow card followed by a red.

With a numerical advantage for the entire second half, Sydney were always going to be the favourites to claim the three points and in the 56th minute O'Neill curled a free-kick over the wall and beyond Thomas Sorensen to give the visitors the lead.

The free-kick was harsh - City substitute Ruon Tongyik barely had a chance to get his hand out of the way of the ball - but Sydney's third goal and Bobo's second again highlighted the hosts' poor defence.

Milos Ninkovic's assist exhibited the perfect combination of vision and technique but Malik will be disappointed with the amount of space he gave Bobo before the Brazilian striker turned and side-footed the ball into the bottom corner.

In the lead-up to this match, City's Tim Cahill had effectively criticised Sydney for putting "11 behind the ball 24/7" and based on fans' reactions to the Sky Blues this term, there would have been many who would have applauded the Socceroos forward's sentiment.

But those who bemoan Sydney's strong defence and well-organised structure miss the point, while also ignoring their impressive attacking prowess that has seen them score over two goals per game.

The premiers of the past seven A-League seasons have all been the side that conceded the fewest goals, while none of those teams have come close to Sydney's defensive record of 0.52 goals conceded per game.

Arnold has created a defence that is effectively unrivalled in Hyundai A-League history and if the competition's quality is to increase, teams will need to be able to defend as well as attack.

Hopefully the other A-League coaches are taking note.