Margaritos experience will pan out big time here.
He was able to fight through an injury against Clottey (where oddly enough Clottey was injured too)
Margarito knows that wining this fight can lead to Cotto.
I think Clotteys a bigger threat then Williams, Clottey was beating early on but Margarito was getting his shots in also. I think Williams biggest issues are 2 things, 1) His chin both Sharmba & Mathysse were able to rock/wobble/move/shake whatever you wanna call it they both got to Williams I think Margaritos power will do more then just rock him. and 2) IMO he appears to tire/get fatigued to the point where his punches start to look like slaps, I've seen this as early as the 3rd round (vs. Pakau) he tends to bend at the elbow and slap the punch instead of extend and snap the punch for the entire round he looses his focus on his strength which is his southpaw stance. If Maragarito can catch onto this and take adavantage of this I think Margaritos got the experience to score some big points.

Williams HAS to maintain a firm grip on his southpaw stance and punch he has to stay busy with Margarito.
Protect his body, he's very tall and someone that tall you attack their body early on look for Margarito to try and get some bosy shots early on so that in the later rounds he try and check the chin. Also Williams needs to do the same attack Margaritos body early on so that he can slow him down so that in the later rounds where Margarito tends to do his best work he isn't as effective.