Padraig Harrington and Phil Mickelson shared the lead at 11 under par after Friday's second round of the Nissan Open in California.

Irishman Harrington, the first-round leader, shot a three-under-par 68 in his debut in this tournament.

Mickelson, who last played Riviera Country Club in 2001, shot the low round of the day with a 65, which included an eagle on the 17th.

Charles Howell, who finished second at this event in 2003, also had a 65 and is at eight under for two days, three strokes behind the leaders.

Pat Perez, Sergio Garcia and English golfer David Howell are tied for fourth at seven under.

It appeared Harrington would have a two-stroke lead going into Saturday's third round when Mickelson failed to get up and down from a bunker on the par-three 16th. Mickelson though made a 14-foot eagle putt on the following hole to rein Harrington in.

"I would have thought there might be more guys up there," Harrington said after looking at the leaderboard.

"It is a tough golf course though."

It is the first time Harrington has played this event and so far has taken a liking to the famed course.

"I'm happy enough," Harrington said.

"It's a big tough ask to follow up a good round. Anything in the 60s was the goal."

Talking about his 17th-hole eagle, Mickelson said: "I had about 287 (yards) to the hole, but only about 260 to the front," Mickelson said.

"So I figured if I could get a good three-wood and land it on the green, the greens have been pretty firm, so it could hit and roll back there. I just flushed it, a nice high three-wood that landed on the green and rolled up there about 15 feet and I was able to make that for eagle."

Mickelson, who hasn't played this event since 2001, is also being won over by Riviera.

"It's a good start, these first two rounds," Mickelson said.

"One of the best players in the world, Padraig Harrington is right there at 11 under and we have a very strong field, a lot of guys five, six, seven under par. So it's going to be a very tough weekend."

David Howell chose this event to begin his tour season and like Harrington he has not regretted it.

"It is a great course," Howell said.

"The first time I played it was two years ago. It was pretty much a wash out, it was so wet. I didn't really pick up on how great a golf course this really is."

The 16th hole had two memorable moments in the second round. The first was the tournament's first hole-in-one. Retief Goosen aced the 165-yard hole with a seven-iron. The eagle actually helped Goosen make the cut. He finished at one under par for two days with the cut set at one over.

The second incident was much stranger. England's Ian Poulter had a four-foot putt for birdie and missed it. For his two-foot comeback par putt, Poulter faced away from the hole and struck the putt with his putter between his legs. He missed that putt as well and tapped in for a bogey.

The three other English golfers in the event had mixed success. Justin Rose shot a one-under 70 to finish even par and make the cut. Brian Davis missed the cut by one stroke. For the second straight week, Luke Donald failed to make the cut. He had rounds of 75 and 72 and missed the cut by four strokes.

Collated second round scores & totals in the USPGA Tour Nissan Open, Riviera CC, Pacific Palisades, Los Angeles, California, United States of America

(USA unless stated, par 71):

131 Phil Mickelson 66 65, Padraig Harrington (Irl) 63 68

134 Charles Howell III 69 65

135 Pat Perez 66 69, Robert Allenby (Aus) 69 66, Sergio Garcia (Spa) 67 68, David Howell (Eng) 67 68

137 Aaron Baddeley (Aus) 68 69, Jim Furyk 67 70, Ernie Els (Rsa) 69 68, Rich Beem 69 68, Johnson Wagner 71 66, Rocco Mediate 71 66

138 Cameron Beckman 67 71, Corey Pavin 72 66, Ben Curtis 69 69, Geoff Ogilvy (Aus) 68 70, Steve Elkington (Aus) 69 69

139 Rodney Pampling (Aus) 68 71, Rory Sabbatini (Rsa) 69 70, David Toms 69 70, Tom Lehman 73 66, Cliff Kresge 70 69, Tom Pernice Jnr. 70 69, Kevin Na (Kor) 70 69, Vijay Singh (Fij) 68 71, John Rollins 70 69, Bill Haas 71 68, KJ Choi (Kor) 72 67, Shaun Micheel 70 69, Briny Baird 66 73

140 Jose-Maria Olazabal (Spa) 70 70, Kirk Triplett 70 70, Bart Bryant 72 68, Jeff Quinney 70 70, Ted Purdy 69 71, Jason Bohn 71 69

141 Charley Hoffman 69 72, Retief Goosen (Rsa) 71 70, Eric Axley 68 73, Lucas Glover 69 72, John Senden (Aus) 71 70, Stewart Cink 70 71, Nick O'Hern (Aus) 71 70, Peter Lonard (Aus) 71 70, J J Henry 70 71, Chad Campbell 74 67, Richard S Johnson (Swe) 70 71, Anthony Kim 72 69, Ryuji Imada (Jpn) 71 70, Tripp Isenhour 70 71, Carl Pettersson (Swe) 72 69, Paul McGinley (Irl) 70 71, Shigeki Maruyama (Jpn) 71 70

142Vaughn Taylor 71 71, Adam Scott (Aus) 72 70, Zach Johnson 69 73, Harrison Frazar 70 72, John Daly 70 72, Kevin Stadler 67 75, Justin Rose (Eng) 72 70, Trevor Immelman (Rsa) 70 72, Craig Barlow 71 71, Tim Petrovic 74 68, Bo Van Pelt 69 73, Scott Verplank 70 72

143 Daisuke Maruyama (Jpn) 72 71, Kevin Sutherland 76 67, Matt Kuchar 71 72, Heath Slocum 69 74, Kenny Perry 70 73, Robert Karlsson (Swe) 69 74, Billy Andrade 71 72, Sean O'Hair 72 71, Mathew Goggin (Aus) 71 72, Mike Weir (Can) 74 69, Ken Duke 71 72, Stuart Appleby (Aus) 70 73

144 Brian Davis (Eng) 73 71, Billy Mayfair 73 71, Brian Gay 73 71, Will MacKenzie 69 75, Daniel Chopra (Swe) 69 75, Nathan Green (Aus) 73 71, Joe Durant 72 72, Justin Leonard 74 70, Ben Crane 71 73, Stephen Ames (Can) 72 72

145 Nick Watney 73 72, Robert Garrigus 72 73, Jeff Gove 75 70, Steve Wheatcroft 74 71, Ryan Armour 77 68, Wes Short jr. 73 72, Camilo Villegas (Col) 74 71, Troy Matteson 77 68, Shingo Katayama (Jpn) 73 72, Ryan Moore 75 70

146 David Branshaw 75 71, David Berganio Jnr. 77 69, Todd Hamilton 74 72, John Mallinger 74 72, Steve Conway 75 71, Toru Taniguchi (Jpn) 75 71, Dean Wilson 74 72, Bob Estes 74 72, Brett Quigley 71 75, Ryan Palmer 74 72, Frank Lickliter II 74 72, Kent Jones 72 74, Jason Dufner 73 73, Bubba Watson 72 74, Hunter Mahan 77 69, Rich Barcelo 77 69

147 Anders Hansen (Den) 72 75, Duffy Waldorf 75 72, David Duval 72 75, Angel Cabrera (Arg) 74 73, Mathias Gronberg (Swe) 72 75, Luke Donald (Eng) 75 72, Alex Cejka (Ger) 75 72

148 Michael Allen 73 75, Joey Sindelar 80 68, Steve Flesch 71 77, Len Mattiace 76 72, Jeff Sluman 74 74, Chris Couch 74 74, Fred Funk 74 74

149 Charles Warren 78 71, Mark Hensby (Aus) 73 76, Woody Austin 75 74, Jonathan Byrd 76 73, Bob Tway 75 74

150 Brad Faxon 74 76, Matt Hendrix 76 74, J.P. Hayes 79 71

152 Robert Gamez 79 73, Ian Poulter (Eng) 77 75

153 Scott Miller 78 75

155 Geoffrey Dean 80 75

159 Ross Marcano 84 75