1)
Why did he say "mi'Kol Tzarah Hitzilani"?
1.
Malbim: When Sha'ul and his men surrounded David and his men and were about to trap them, a messenger came and told Sha'ul that Pelishtim [invaded and] spread over the land. Sha'ul went away from pursuing David.
2)
What is the meaning of "uv'Oyvai Ra'asah Eini"?
1.
Radak: My eye saw what it wanted. The same applies to "va'Tabet Eini b'Shurai" (92:12).
2.
Malbim: Even though my eye saw my enemies, I did not need to fight with them and kill. You saved me also from this! This was the primary miracle, that I was not saved via war and bloodshed.