I've had problems like this gaming if my CPU or GPU aren't cooling properly.
Basically things run OK until circuits get hot and then freeze up or performance would degrade noticeably.
I'd check you machine innards to see if you see a lot of dust. Especially around the CPU heatsink or the heat sinks on the GPU on your vid card.
There is something called Intel Extreme Tuning Utility you can download that can run a stress test on your CPU and monitor the chip temp and see if you are getting any thermal throttling. That's worth a check.
Do you have a spare video card to swap out to see if it still does it? After you've been playing, are the fans turning ok on the chip heatsinks?
One time the fan on my video card was toast and not working. Another time I had a ton of dust on my CPU heat sink and the thermal paste had dried out and wasn't conduction well.
That is what I'd check first. Good luck.