really odd situation - ball strikes ball into hazard, not sure of ruling

[johnclayton1982]

I was playing a quick round last night at my local course after work with two friends.  On the par 5 5th hole, my third shot ended up on the green from a seven iron.  My playing partner, who got into some trouble in the woods on his drive, came in onto the green with a long hybrid as his third shot.  His ball actually hit my ball, causing it to fly off at a 45 degree angle, hit a downslope on the green, and roll into a greenside bunker.  His ball went the other way a ways, and ended up on the fringe.

What do you do in this situation?

I hit the ball from the trap and made bogey (shot out of trap plus two putts).  I also put a provisional down where my ball was and putted out for par (just two puts from my original ball location b/fore playing parters ball knocked it into a sand trap).

The reason I decided to post and ask is (1) curiosity, but more importantly, I shot my lowest round ever, and the first time breaking 90 (everything was working for me somehow).  I shot an 86 with the provisional two-putt par, and an 87 with the ball being knocked into bunker then playing it out.  Since it might be a while before I beat that score again - which do I take as my "lowest round" under the rules, the 86 or the 87?

Note: I want to play it straight, so that I can always compare my scores later.

Thanks all, and thanks to all who helped me with my long irons in the other thread.  This is a good site.

[Wigginlsu]

This happened to me about a year ago on 18 at a local course. My friend hit his drive down the right side along a long lateral water hazard and my drive in probably a 1 in a million shot hit his into the water leaving mine dry. He dropped and played out and when we asked the pro in the clubhouse he said the correct ruling was to play my ball from where it stopped and place my partner's ball (new one in this case) as near to its original spot as possible.  Not sure what the rule # is but it made sense and since we've never encountered that again we've just kept believing that's how it is played.

[Zeph]

Quote:

Rule 18. Ball at Rest Moved

18-5. By Another Ball

If a ball in play and at rest is moved by another ball in motion after a stroke, the moved ball must be replaced.

The ball already on the fairway and being bounced away is replaced. The ball that moved the other ball is played from where it lies.