And then Chuck Thompson shuts up, like an announcer should in that situation.
A much more understated example than most of the others in the thread, but the all-time classic in snooker commentary was “Whispering” Ted Lowe’s “For those of you watching in black and white, the yellow is behind the green”.
Another of my favourites (also from snooker) was when Peter Ebdon, known for his somewhat eccentric shot selection on occasions, attempted to pot a long red with a “deep screw” (fnarr) shot. In this shot the cue has to hit the white right at the bottom. Ebdon did this rather too much, causing the white to jump about two feet above the table, bounce over two other balls, and pot a red at which he had not been aiming. John Virgo’s commentary on the replay was “Well, would you believe it - it were like the Grand National!”. Ah well - guess you had to be there.
I think this has already been responded to by a couple of others, but as a Dodger fan, it was many years before I heard what I consider to be Jack Buck’s “alternate” call. 
The linked recording is most assuredly Jack Buck.
Vin Scully said, as all Dodger fans know, “In a year that has been so improbable, the impossible has happened!”
According to the Wiki transcript, which I believe is accurate, Hodges also said it four times, then once more after some additional commentary.
In the first generation after 1951, before the recording had circulated widely, and when misinformation was harder to debunk, many people remembered and insisted that Hodges had screamed “The Giants win the pennant” for several minutes. Not so, we now know.
For Flyers fans, here’s Gene Hart:
I loved it because it began with 3 or 4 seconds left in the game. That’s why the first sentence is in a very assured future tense.
If only it weren’t from (sigh) 37 years ago.
Jon Miller, KNBR 680, May 27, 2003. San Francisco Giants v. Arizona Diamondbacks
That was the worst base running in the history of the game!
Another San Francisco gem, Joe “The Band Is Out on the Field” Starkey calling Terrell Owens’ “The Catch 2”, not the best quality, silly NFL Films enforcing their copyright.
Six “Owens!” by my count.
I haven’t seen that one in a long time – it makes my day. 
Who ended up winning that game?
The Giants, 4-3 in 13 innings.
Harry Carpenters famous outburst at Bruno/Tyson here:
(at around 04:20)
Jim McKay
“They are all gone.”