- Wimbledon, Day 11
Serena books latest Wimbledon final appearance
Sixth seed Williams will face world No. 3 Agnieszka Radwanska in Saturday's final, as she aims to become All England Club champion for the fifth time in her seventh final appearance.
She will also have the chance to equal the number of titles won in SW19 won by her sister, Venus.
Williams was forced to dig deep in order to defeat Azarenka, the second seed this week at the All England Club. In the end she needed a tiebreak to clinch a fraught encounter, running out a 6-3 7-6(6) winner in a little over 90 minutes.
It was Williams' serve that ultimately carried her through to victory - with her ace down the middle that ultimately gave her victory also serving to break her own record for aces in a women's singles match, 24.
"I've been working so hard, I really wanted it," Williams told the BBC. "She was playing well and I got a little tight in the second set. I was looking too far in the future. I was so close, but I can't do that.
"I was happy to get through that second set tie-break."
Azarenka can otherwise feel frustrated to have been defeated, as one crucial mistake ultimately cost her the first set before she was edged out in the second stanza. Serving at break point down at 3-4, Azarenka opted for a less-than perfect drop shot that Williams feasted on with glee - burying it down the line to make the first real move of the match.
That was enough for her to claim the first set - with her booming serve keeping her out of real danger - before she kicked off the second set with a confidence-boosting save against Azarenka, having fallen into a 15-40 hole.
Azarenka was clearly deflated at throwing away a great opportunity to break and that disappointment cost her - as Serena sprung into life in the next game to break clear and leave her just needing to hold serve to confirm her spot in the final.
Azarenka, however, was not going to go quietly - and soon broke back at the second time of asking after forcing Williams, suddenly uncertain with her groundstrokes, into knocking a forehand wide.
Both players served out to 6-6 from that point, setting up a decisive tiebreak. And it was Williams who would take it to claim the match, spurning one great match point opportunity on Azarenka's serve before firing an ace down the middle that left nothing in doubt.
Williams will now face Radwanska, after the Pole defeated Angelique Kerber in the first match of the day.
"She's doing unbelievable," Williams said of her opponent. "She's playing so great. Wow, she's going to get every ball back."