Aga had no serve whatsoever while Lucic was playing lights out on both serve and return. Wasn't even remotely close. By the end of the match Aga was likely ~50% points won behind 1st serve.
I really thought Djokovic had saved it during the third set when Istomin began cramping - he'd been poor but after 3 hours his opponent's legs were going. Then it got crazy. Istomin was super clutch behind his serve, but still, seeing Djokovic make so many routine errors when it counted was strange, and he didn't connect with his forehand much. His second serve was doing little all match. Basically, his defense was there, but his attack was weak and he looked scared to commit on his forehand, while Istomin won the important points. Amazed he held up physically for five hours.
The bottom half of the draw is super open now - it was probably the softer half even with Djokovic. In Djokovic's section Dimitrov and Gasquet will face off knowing they'll face either Carreno-Busta or Istomin in the 4R for a place in the quarters. There they could face Thiem or Goffin (maybe Karlovic?). Nadal, Raonic or Zverev likely awaits the winner for a place in a Slam final. Of all those players, only Nadal and Raonic have ever been to one before, and Nadal hasn't been there since 2014.