Team 8 jumped out to a big lead with their double assassin comp against Team Impulse's double ADC comp. A few poor engages lost T8 their advantage, and TIP won a series of teamfights and pushed down two inhibitors. TIP decides to rush Baron instead of waiting for their two lanes of super winnions. We all know what happens next.
Link to Video
While Baron Nashor deals damage and shreds resistances, TIP were mostly healthy and had solidly won the last few teamfights. It looked like TIP's comp had outscaled T8's. It's not uncommon for the team that's ahead to win a contested Baron fight, especially if they secure the Baron. Indeed, most of T8 played the fight poorly. Why did TIP lose this fight 0-3?
There were three reasons T8 won the fight:
1) Maplestreet put on his carry pants and almost single-handedly won the fight.
2) Dodo hit some really crucial CC on Ezreal.
3) TIP (especially Apollo) had appalling target selection. They let securing Baron supercede winning the teamfight, and it showed.
Let's see what happened:
The start of the fight. Both teams have vision of each other. TIP has a summoner spell advantage. T8's assassins and Rek'sai don't have their Flashes. This hinders their ability to reach TIP's back line, especially with Fizz's distance from the fight. TIP's Corki does not have Heal.
T8's Reksai built very defensive and itemized plenty of armor. Corki is nearing full build, but his defensive item is a Spectre's Cowl.
In the previous image, we saw Janna use Tornado (6 second CD with max CDR). Here, Maokai uses Twisted Advance (5.4 second CD with max CDR) on Rek'sai. Both are used to prevent a possible smite-steal. Ezreal and Jarvan are inside the pit, while Corki moves out to hit Rek'sai.
About 1 second later, TIP take Baron.
Leblanc uses two Chains on Maokai. Nami sends a good Tidal Wave across the narrow Baron pit opening. Perhaps in response to this, Corki moves up the river away from the Baron pit opening. Graves puts a Smokescreen toward the upper part of the Baron pit opening and goes after Corki.
A moment later. Leblanc burns her entire combo (Chains, ult Chains, Sigil) on an ulted Maokai. It takes off half his health with more chain procs to come. Graves starts a Buckshot which will strip the Bloodthirster shield off of Corki. Corki moves further up the river to get out of Smokescreen. Ezreal begins to ult.
A moment later, Corki turns to shoot a rocket -- towards Rek'sai. Graves wastes no time shooting Corki. Corki's movement seems to have taken him outside of Maokai's ultimate.
Janna pops the Iron Solari shield. Ezreal's ultimate casts, and he's immediately knocked up from Nami's Tidal Wave. Both Maokai and Rek'sai are pretty low.
Here we see the difference in target selection. While Graves is focused on Corki, Corki turns back toward Rek'sai and Leblanc.
And here's where the fight is decided. Since the last picture, Corki has completed launching a Phosphorus Bomb toward Rek'sai and Leblanc that will end up hitting no one. Graves auto-Quickdraw-auto'd Corki. Ezreal's focusing damage on Rek'sai, but Nami cast an Aqua Prison towards him.
Graves hits Corki again, bringing him low. Corki realizes the danger and panics, milling about for a fraction of a second. Nami's bubble lands on Ezreal and saves Rek'sai.
Graves's Collateral Damage brings Corki very low, and Corki flashes into the Baron pit. Fizz finally joins the fight, only for his ult to pop Jarvan's Banshee's Veil and fall to the ground. Leblanc tries to Distortion into the fight, but Janna begins her ult.
Graves Flashes after Corki, who's trying to run to the wall. Ezreal finally regains control and turns towards Graves. On the other side, Leblanc's Distortion was canceled by Janna's ultimate, and TIP moves away from Fizz's ultimate. Janna's ultimate also knocks back Fizz. Jarvan tries to kill Rek'sai instead of peeling Fizz.
Graves kills Corki, and Ezreal is trapped between Fizz and Graves. Rek'sai survives Jarvan's Cataclysm -- presumably Nami healed him. Fizz ult hits no one.
Fizz and Graves both jump on Ezreal. Janna Exhausts Leblanc, which maybe keeps Maokai alive a bit longer but was a poor choice compared to Fizz or Graves.
Ezreal tries to Arcane Shift but too late. He's blown up. Maokai's Twisted Advance finally comes off cooldown. Janna's Tornado comes off cooldown at about the same time.
T8 goes on to kill Maokai. Janna and Jarvan both escape (Jarvan not having used his flag-and-drag combo during the fight), but T8 take the Nexus.
Let's recap. Baron did a few things: it made positioning difficult for TIP, probably shredded some resistances, and kept Ezreal and Jarvan out of the fight for a few seconds (the fight lasted about 9 seconds total). On the other hand, Fizz was late to the fight and whiffed his ult, and Leblanc didn't have a big impact either.
More importantly, TIP forgot that taking Baron doesn't win you the game. Winning a teamfight at 47 minutes wins you the game. Baron baited TIP into focusing Rek'sai. Zoning Rek'sai from Baron cost TIP crucial cooldowns which could have been used to peel for their carries. Trying to kill Rek'sai cost Corki precious spells and attacks that could have been used to duel Graves. Maplestreet didn't make the same mistake and focused Corki, then Ezreal. That's what won T8 the game.