Calcavecchia, who started on the inward half at Hazeltine National Golf Club, shot 4-under 68 to move to 6-under-par 138 through 36 holes. Hes tied with 1997 British Open champion Justin Leonard, 2001 U.S. Open champion Retief Goosen and International winner Rich Beem.
Leonard, who finished runner-up to Davis Love III in the 97 PGA at Winged Foot, made seven birdies and one bogey in shooting the lowest round of the event, a 6-under 66.
Beem also fired a 66, birdieing the last after pushing his tee shot into the right gallery.
Goosen's final hole was even more exciting, as he missed the green but chipped in for birdie and a 69.
'I didn't have a good lie, but I had lots of green to work with,' Goosen said of his chip shot. 'I played the back nine great and, obviosuly, to chip in on 18 was a bonus.'
Rain started to fall as the morning groups neared the clubhouse. Overnight showers are expected, as is early morning precipitation Saturday. Day 3 is also expected to bring with it 30-40 mph winds, adding to the importance of Fridays round.
'I think we will see the real teeth of this golf course and I'm looking forward to that,' said Leonard, a Texas native. 'I want to see it play as difficult as possible.'
Overnight leaders Jim Furyk and Fred Funk, both of who shot first-round 68s, are among the afternoon tee times. Furyk teed off at 1:25 PM local time, while Funk went off at 2:35 PM.
Tiger Woods, who opened in 1-under 71, started his second round at 2:05 PM.
Lightning delayed play by three hours on Day 1, leaving 39 players to complete their second rounds Friday.
Calcavecchia wasnt one of them. He escaped under the cover of darkness, finishing his final hole when the horn sounded. He posted a 2-under 70, and then went right back at it about 12 hours later.
The 10-time tour winner started his second round on the 10th tee, and birdied 10 and 12 before dropping a shot at 13. He more than atoned for that mistake by chipping in for eagle on the par-5 15th, and then birdieing 16 and 18.
The front nine wasnt as prosperous, as he shot 1-over 37. Twice he made bogey, and twice he birdied the next hole. After making a 6 on the par-5 seventh, Calcavecchia nearly aced the par-3 eighth. His tee shot from 185 yards landed a foot from the hole.
His round ended on a sour note, however, as he missed the green at the par-4 ninth and failed to get up and down.
'I've always been streaky, sometimes I'm streaky bad,' Calcavecchia said. 'I stay aggressive and I think that's why I'm able to shoot some really low numbers.'
Calcavecchia has been battling a chronically bad back. He was seen spralled out in the fairway Thursday, stretching his lumbar region.
'Better today than yesterday,' Calcavecchia said of his back. 'I don't know what happened, I excercised the other day and threw my back out.'
Calcavecchia has one major on his resume, the 1989 British Open. He defeated Greg Norman and Wayne Grady in a playoff at Royal Troon.
This is Calcavecchias 50th major start since hoisting the Claret Jug, and the big events have seen little results. The 42-year-old has but three top-10 finishes in majors since his British triumph, two of which came last year. He tied for fourth in the 2001 Masters and recorded the same result later that year at the PGA in Atlanta.
This year, he missed the cut in both the Masters and U.S. Open, and tied for 80th ' out of 83 to make the cut ' at Muirfield.
'That'd be the ultimate,' he said about winning a second major. 'I wouldn't think coming into this week, that it was looking too good, certainly my form hasn't been great. But that's the way I play. Any given week I show up and I hit three or four good iron shots in a row and make some putts, I can get hot, get going.'
While his rush up a major leaderboard may be a bit of a surprise, the fact that he reeled off four birdies and an eagle in nine holes should not be.
Calcavecchia set or tied seven PGA Tour scoring records in winning the 2001 Phoenix Open ' his last tour victory. He made a tour record 28 birdies in setting a 72-hole aggregate record of 256.
He also shares the back-nine scoring record at the Masters, shooting 29 in 1992.
Unlike his fellow Open champion, Leonard has fared well in the majors since his maiden triumph.
The 30-year-old lost in a playoff to Paul Lawrie in the 1999 British, and has finished in the top 20 in all three majors this season. He also won the '99 Players Championship.
Beem is making his fourth career major appearance, and first of the season. He has two missed cuts and tie for 70th (1999 PGA) in his three previous starts.
'I don't have a lot of experience at this. I'm coming off a great week two weeks ago at the International so my confidence is high, but there's a lot of golf to be played,' Beem said.
Full-field scores from the 84th PGA Championship