Guess riven is my lucky charm.
Fighting panth as riven is such a pain in the ass.
Erm, bait spears and shield them off? Panth goes out of mana easily and he can't win a direct trade if he couldn't harass you down some. You outscale Pantheon so the early levels are rougher but it should be in your favor start to finish.
Gives me hope you just said that. My first time playing Riven I got matched against a Pantheon and I just didn't know what to do.
I'm copying off guides and building BT+GA but I find with her the same problem I find with all AD champs, buying that BF Sword is just painfully hard early game, and buying a couple Doran's Swords pushes it so far back it makes you feel like it takes forever...
Boots x3 (if not needed for an invade / counterinvade, recall around 1:28 to grab an extra pot if you expect to trade a lot in lane). First back around 1000 gold for 2x Doran's, 1-2x Wards (X pots) and then BF Sword around the 15m mark. This will depend on how well you cs, however, so I'd work on that. 10 cs/minute etc. etc, 120-130 should be fairly easy for the 15m mark unless you're being ganked a lot (or forced to be passive).
By the way, what's the stance of Warmog's on Riven? Or her build in general? I'm following this guide at the moment:
http://solomid.net/guides.php?g=16914
I'd probably never get Warmog's. Your survival is the AD scaling on your Shield (and the damage you deal) so Frozen Mallet is the better HP item. That said, I wouldn't build FM all that often either as you can get better survivability through other means (e.g., Randuin's) and the proc isn't super necessary for Riven. Basically:
Boots2, BT, GA, situational things (e.g., LW for Damage, Maw for anti-AP, Randuin's for anti-AD). If you're vs AP in lane, Hexdrinker (but not Maw) before BT.
Also of note, I'm a fan of 19/11 for Riven. The extra -2 damage/hit really helps for low level trades by reducing minion damage and also makes freezing lane easier on you. Executioner is good but you have a good ranged execute as is and any damage dealt in the trigger range should be a kill for you regardless.