Actually it was Giant. What was really impressive is not that you meleed pretorians but that you managed to stay alive.
At least I do not remember that you would have been grabbed.
ps. I do not know how could those pretorians miss a large krogan in hot pink armour 
Thanks. They're used to seeing the pink on the inside, thus they think I'm already dead. 
Through trial and error, I've gotten pretty good with avoiding praetorian sync kills with krogans:
1) Nearly always one free melee when they start their lazors. Two is risky, but possible.
2) Juggy teammates (like I think we had on Giant) are actually useful for drawing claw attacks and aggro in general.
3) Starting a melee while the crab jumps is another freebie
4) If you're team has a strong DPS player on it, you can get away with a lot. If I've got a Claymore GI on my flank I'll risk the grab and trust they'll stagger it out of the sync animation.
5) End of waves! The more of the team targetting the crab, the safer my krogan melee is. Also, the consequence of getting crunched is less hurtful to the team.
6) Ramps! Dagger has a few nice ones. And a properly setup krogan has enough DR and protections to weather lots of bs claw attacks on said ramp.
7) Melee attacks that break the crabs barrier gate have a few tactical advantages. Higher damage from the outset since you're not going up against armor's 25% resistance to krogan heavy melee. Plus, you can be surer that the crab's stagger isn't on cooldown so you've got a better change at knockback or for a teammate to save you from a sync kill.
8) All krogans except the warlord can use a heavy melee to charge away from the crab and get out of grab range. It's possible with the warlord too, but is definitely harder. If you can lock onto a nearby mook, you'll get even farther away.
9) The Graal is an excellent companion for the melee krogan. Keep it charged while you melee and release it when the crab tries to stagger you. Yet another damage spike that might stagger the beast.
10) Both my krentinel and kroldier run no passive builds, so I'll always try to fire off a power and a grenade as I engage for additional damage spikes.
I'd apply this list to atlases, scions and even brutes.
Phantoms are both easier (squishy) and harder (bs sync mechanics).
For banshees there is only one rule: avoid when moving, smash when standing.
I don't play the Destroyer much. 