It should be easy to write a tactical preview of these two teams, because they've been so stable and they've played each other so much. RSL aren't appreciably different (tactically speaking) from the 2009 team that beat LA in the MLS Cup final. LA are very close to being the same group that won the Cup/Supporters' Shield double in 2011.

We have years of tape on these clubs.

We know Jason Kreis still prefers to play his diamond. We know Bruce Arena still likes to go with what is more of a flat midfield four (which comes nowhere close to doing LA's tactical structure justice).

But somehow, I don't have a feel for how this one (9 pm ET; ESPN) is going to turn out. Familiarity in this case could breed some real experimentation.

Here's why:

Keane and Donovan are shape-shifters

Landon Donovan and Robbie Keane are both forwards. Can't say what kind, though, because their role is defined by how, in any given moment, they are orienting themselves with regard to one another.

Stopping the Galaxy has been hell since Keane arrived in mid-2011 not because he is an individual maestro capable of unlocking any defense, but because he and Donovan seem to share one attacking brain out there, able to instantly recognize where the time and space will be, then play either a primary or supporting role in opening up said time and space for each other.

Am I the playmaker right now, or am I stretching the defense? These decisions are made instantly, and in almost perfect concert.

It's particularly breathtaking in transition:

Donovan has all that space, trailing the play, because Keane has put his back to the goal like a target forward and drawn three defenders. It's pragmatic from Keane (something he's not given enough credit for), and he's willing to do that bit of donkey work because he knows Donovan will make the right movements behind him.

That's Donovan working off of Keane. Here's Keane working off of Donovan:

My favorite part of that gif is Keane's petulent little kick at the turf when he sees Gyasi Zardes cross for the back post. Then he instantly realizes it's Donovan making that run, and knows there will be a return pass across the box. So he strolls to the top of the six for a tap-in.

Donovan's aggressive run occupied the defenders in this case, allowing Keane to trail the play and poach the goal. It's a nearly complete role reversal from the goal against Vancouver.

Can't stop one of these guys or the other. Got to stop both together.

Getting to the second ball first

Here's a thing about those two goals above: both of them happened after the LA midfield closed down space and won a second ball. They do that a lot, and when it happens, they almost immediately play into the attacking third:

Team Passes, Final 1/3 Accuracy, Final 1/3 LA Galaxy 5041 66.51 Real Salt Lake 4664 66.55 Portland Timbers 4568 65.94 New England Revolution 4392 62.39 Sporting Kansas City 4205 61.85 Houston Dynamo 4093 59.57 Seattle Sounders FC 4085 63.6 New York Red Bulls 4073 64.87 Colorado Rapids 4041 60.95 San Jose Earthquakes 4001 59.21 Columbus Crew 3900 60.03 D.C. United 3874 61.07 Toronto FC 3873 58.02 Vancouver Whitecaps 3846 61.93 Chicago Fire 3721 60.2 Philadelphia Union 3628 58.05 Montreal Impact 3522 59.06 FC Dallas 3437 59.99 Chivas USA 3127 57.85

The Galaxy are dominant in those stats because of Juninho, Marcelo Sarvas, wingers who force passes into bad lanes, and aggressive fullbacks who push up to intercept low-percentage plays.

RSL are very good at avoiding that first wave of pressure and choosing higher-percentage plays. Plus they have a selection of technical, confident midfielders able to receive even when in heavy traffic.

Kreis will, as almost always, go with the midfield diamond with this one. But don't be surprised if he drops Luis Gil -- a good attacking player -- for Yordany Alvarez at d-mid, then pushes Kyle Beckerman out to the right flank.

Sacrificing Gil means RSL won't get as much penetration into LA's third of the field, but in the away leg against the two-time defending champions, a prudent coach goes with another midfield ball-winner because winning balls at midfield is LA's lifeblood. The rule of the day has to be "stop them from doing what they're best at."

So expect RSL to play a bit deeper and try to slip one of their speedy forwards (my guess is Robbie Findley) behind the comparitively slow LA central defense, or have him loop around the flanks for diagonals, then watch midfield attackers Javier Morales and Ned Grabavoy advance behind the play.

It's a different look for the diamond, but one that Kreis hasn't been shy at hinting at. And if it means his team has a better chance at slowing down Keane & Donovan, then he shouldn't be shy of using it, either.