http://revach.net/article.php?id=4410

Section: Moadim   Category: Megilas Esther
Megilas Esther: Rav Yehonoson Eibshitz - Who Was Haman Really After, The Yehudim Or Mordechai?
Rav Yehonoson Eibshitz says that when things are going well for a Rasha, the gemara Megila (6b) says that you should stay out of his way.  If so why did Mordechai go out of his way to antagonize him and show him he refused to bow?  He should have made himself scarce.  The pasuk says, "Vayivez B'Einav Lishloach Yad B'Mordechai Livado Ki Higidu Lo Es Am Mordechai".  Haman didn't want to harm Mordechai because he knew what nation he was from.  If he wanted to kill all the Yehudim what was disgraceful about starting with Mordechai first?

Rav Yehonoson Eibshitz explains that Mordechai knew through a Malach that Haman wanted to kill all the Yehudim and was planning to slander the Yehudim in order to gain permission from Achashveirosh for their murder.  He wanted to sabotage his plan by antagonizing Haman to the point where Haman would kill him.  In order to kill Mordechai, Haman would need permission from Achashveirosh.  Once Haman killed Mordechai he would have no credibility with his slander on the Yehudim since Achashveirosh would think it was part of his revenge on his sworn enemy Mordechai.  In essence Mordechai was sacrificing his life and causing his own demise in order to save the Yehudim.

Haman understood this.  Which is why the pasuk tells us that when Mordechai antagonized Haman, Haman wanted to kill him.  However because he knew which nation Mordechai came from he controlled himself in order not to sabotage his own grander vision.