[Mid-Air Collision (???)]

Greetings.

The other day while controlling at PHL, I was penalized for a mid-air collision (Oh, the humanity! 🙂 ) of two incoming flights. They were cleared on land on Runway 26 and still a few miles out. I probably could have avoided this by diverting one to 27L or 27R. But...am I wrong to presume that TRACON/Approach would sequence incoming flights safely?  I can't recall the separation but they were NOT nose-to-tail close on radar. Any guidance would be appreciated. I prefer to avoid future "Mid-flight Passenger Exchanges." 😉  Leon

[Want to know how does an airport operate? (USA only airports)]

Thanks Pete. The information on the airports will really add a new level of realism to my time on the Tower sim without getting overly complex.