Flesh is making his 12th senior start after turning 50 in late May.
''It's kind of an awkward golf course off the tee, so you need to be decisive about what club you are going to hit and if you can hit it in the right places, you can make some birdies,'' Flesch said. ''You have to pay attention out there. There are some tough tee shots out there and some awkward greens, so you can't put yourself in the wrong place.''
The four-time PGA Tour winner had four birdies in a five-hole stretch on Bear Mountain's Mountain Course and capped the bogey-free round with a birdie on the par-5 18th.
''I hit a lot of good tee shots and set myself up for a lot of short irons,'' Flesh said. ''I didn't make a lot of putts early one, but I got it going in the middle of the round and ran off a few. It surprised me how much the golf course has dried out just in the last few days.''
Smith also closed with a birdie and had six birdies in a seven-hole span before bogeying the par-3 14th. He has one senior title.
''Pretty easy eagle on No. 1 after a 3-wood,'' Langer said. ''I pretty much stiffed it on the next two holes, so suddenly I was 4 under after three. I played pretty solid, although there were a couple of loose shots. Overall, it was pretty decent. I had a couple of chances coming in, but didn't make any putts.''
The German star won three of the tour's five majors and is tied with Scott McCarron for tour victory lead with four.
''The greens have really toughened up and are really firm and really fast,'' Langer said. ''We don't get conditions like this very often, so you have to be aware of it. You have to be on your toes and know what greens are firm and what fairways are running out.''
Daly won the Insperity Invitational in May in Texas for his first senior title. The fan favorite eagled the par-5 12th.
''Over the years, Canada has been just a wonderful place to come and play,'' Daly said. ''I always feel the support of the fans. I always love the fans and love playing for them, but it's a hell of a lot better when you are playing good, however.''
Kelly took the Boeing Classic three weeks ago outside Seattle for his first tour victory.
''I wasn't very happy with the way I started the year, but since I won, I have started to play much better,'' Kelly said. ''Took a change of putters, a change of irons, a change of drivers, a change of shoes to play better. These courses are not pitch and putts. They are tough golf courses, period. You need to shoot low every single week. You need to make putts.''
Canadian Stephen Ames topped the group at 66.
Defending champion Colin Montgomerie opened with a 70. He won last week outside Tokyo in the 50-and-over tour's first event in Japan.
McCarron had a 71. He lost a playoff to Montgomerie last year at Bear Mountain, and tied for second last week in Japan after winning three of the previous six events.
Nick Faldo shot 73.