THIS is a crucial round for many teams, and I've picked one match from each day in round five that will be critical in shaping the season.

Port Adelaide enter Friday night’s match against St Kilda brimming with confidence after defeating Hawthorn last week in what Port coach Mark Williams described as his club's best ever home-and-away win.

St Kilda go into the game undefeated and on top of the AFL ladder. 

There isn’t a lot to separate these two teams and both have every reason to believe that if they play to their strengths their best will be good enough to win.

But with inclement conditions forecast the weather may play a deciding role.

Both teams have clearly identified starts as critical to their early season form. Port have won the first quarter in all of its three victories and St Kilda has dominated its opening terms so far, winning all four.

Port gets its hands on the football more than any team, averaging 438 possessions in its three wins – in its only loss to the Eagles in round two the Power could only manage 380 disposals.

St Kilda, on the other hand, is simply not allowing its opponents to win enough of the football, conceding only 360 disposals a game.

Port Adelaide will need to find time and space to reach their required 400-plus possessions otherwise the Saints will have won a crucial statistical battle.

Port is ranked fourth in attack and in each win has scored more than 100 points, but they come up against the game's most frugal defensive outfit on Friday.

St Kilda has the best ranked defence – and more significantly it has only allowed opposition teams inside-50 an average of 38 times.

It's worth pointing out that Hawthorn conceded an average 43 entries last year. No team has kicked more than 10 goals against a defensive unit still without Max Hudghton and Matt Maguire in 2009.

Both teams accumulate the ball with contrasting styles. Port's game is built on winning uncontested touches whereas St Kilda leads the pack in contested possessions.

Port relish the wide open spaces of AAMI Stadium but with heavy rain forecast will need to take its game inside against a side that thrives on physical football.

Both play attacking footy, but in difficult conditions that require teams to adopt a simple game plan, uncontested football won’t stand up.

Port takes on a rampant outfit whose four wins have been as much about attacking, free-flowing football and kicking winning scores as it has been about harassing, pressuring, chasing, intimidating and tackling the opposition.

St Kilda’s insatiable appetite for the physical side of football is best reflected in the fact that it is averaging 70 tackles a game.

My tip is the Saints to win by 24 points.

Hawthorn v West Coast
I doubt anyone who follows football would have predicted last year's premiers would be sitting 13th after the first month with just one win to their name.

The Hawks have been hit hard by injuries and have struggled to recapture that intoxicating brand of football that took them to the top of the mountain last year.

Hawthorn take on West Coast in Tasmania on Saturday afternoon and, if the Hawks harbour any hope of a top-four finish, this is a must-win game.

The Eagles are coming off an outstanding win against the Western Bulldogs at home and, if they can manage to replicate that performance, it is conceivable that another massive upset could be on the cards.

Making the Eagles’ job harder is the fact that they have not won an interstate match in 13 attempts.

West Coast will never get a better opportunity against a Hawthorn outfit down on confidence, low on premiership players and teetering on a slippery slope as its tries to get a spluttering season going.

West Coast’s record at Aurora Stadium is two wins from four attempts and, with a third win beckoning, the Eagles could put a serious dent in Hawthorn's plans for September.

Western Bulldogs v Carlton
This is an important match on Sunday with both teams looking to rebound from disappointing losses.

The Dogs will welcome a home game and a seven-day turnaround after their return flight from Perth, whereas the Blues got a healthy dose of reality last week against the Swans in Sydney.

If Hawthorn were to lose to West Coast the Bulldogs have a golden opportunity to steal an early march on the Hawks and go three games clear of last year's premiers. And if St Kilda defeats Port Adelaide, the Dogs will have a handy one-game buffer over Port.

Carlton is an improving side, but it’s a little premature to say it possesses The Fab Four (Nick Stevens, Bryce Gibbs, Marc Murphy and Chris Judd), and if we are to believe they're ‘coming’ as the billboard suggests, then this is a game they must win.

The views in this article are those of the author and not necessarily those of the clubs or the AFL.