According to R’ Eliezer of Worms, the verse points out that Mordechai came to Achashverosh without an invitation, and this shows his new power.
M’nos HaLevi writes that there was a rule prohibiting approaching Achashverosh without invitation (see Esther 4:11). According to him, this rule died together with Haman. The entire point of the rule was to strengthen Haman’s influence on the king, virtually guaranteeing that his was the only voice whispering in the king’s ear.
Unlike the opinion of R’ Eliezer of Worms, he further adds that Mordechai was called by the king.
In fact, according to the Malbim, the verse implies that Mordechai was promoted.