Irish duo advance to match play last 16
Clarke completed a comprehensive 6&5 win over Germany's Alex Cejka while Harrington was next to go through with a 3&2 win over Bob Estes.
Colin Montgomerie made it four British and Irish players into the last 16, surpassing the previous best of two at the same stage in 2000.
Clarke, the winner in 2000, survived the second longest match in the event's history in the first round, winning at the seventh extra hole against Eduardo Romero.
But the Irishman was never in danger of a repeat when Cejka went to the turn in 40 and Clarke only needed to be level par when the match came to an end on the 13th.
"I'm pleased to get through, I played okay but not great," said Clarke.
"Alex had one of those days where everything went wrong for him.
"Everything he seemed to try didn't come off and when you get into a position like that in 18-hole match play, it's very difficult.
"I think the score flatters me a little bit but I'll take it.
"I'm delighted to have come through so quickly considering we have to go out again."
Montgomerie produced easily the best golf of the week as the British and Irish challenge gathered momentum
Montgomerie was seven under par for 14 holes in beating Stewart Cink 6&4 as he joined Ian Poulter.
Poulter led the way with birdies at his last two holes to thrash Duffy Waldorf 7&5 at La Costa, and on the same hole minutes later Montgomerie, who needed extra holes to see off Nick Price in Wednesday's first round, birdied four of his first six and raced to the turn in 31, the best of the week.
Poulter was aided by a poor performance from Waldorf who conceded two holes and bogeyed two others on the front nine, but the young Englishman also found his putting touch after reverting to an old putter.
"It was a very solid performance today," said Poulter, who is making his debut in the event.
"I played exactly the same way as Wednesday, hit fairways and greens, and I don't think I missed a fairway all day.
"Duffy did miss a couple early on which meant he had to chip out sideways and he was on the back foot from the word go.
"It was nice to have that momentum, on the tee first all the time and hitting the fairway all the time, and when you are on top that's almost all you have to do."
Montgomerie takes on Australian Stephen Leaney in the third round after he overcame US Masters champion Mike Weir 3&2.
Clarke is up against Kenny Perry, Poulter faces John Huston and Harrington will play Ryder Cup rival David Toms.
Sweden's Fredrik Jacobson will play defending champion Tiger Woods after they beat Thomas Bjorn and Trevor Immelman respectively by 5&4.
Second round of the WGC Accenture Match Play Championship, LaCosta Resort, Carlsbad, California
(USA unless stated)
Phil Mickelson (USA) bt Ben Curtis 7&6
Ian Poulter (Eng) bt Duffy Waldorf 7&5
Darren Clarke (Irl) bt Alex Cejka (Ger) 6&5
David Toms bt Shaun Micheel 4&3
Padraig Harrington (Irl) bt Bob Estes 3&2
Tiger Woods bt Trevor Immelman (Rsa) 5&4
Fredrik Jacobson (Swe) bt Thomas Bjorn (Den) 5&4
John Huston bt Peter Lonard (Aus) 1 hole
Kenny Perry bt Steve Flesch 1 hole
Colin Montgomerie (Sco) bt Stewart Cink 6&4
Stephen Leaney (Aus) bt Mike Weir (Can) 3&2
Vijay Singh (Fij) lost to Jerry Kelly 4&2
Davis Love III bt Fred Couples 3&2
Stuart Appleby lost to Chris DiMarco at 19th hole
Chad Campbell bt Loren Roberts 3&1
Adam Scott (Aus) bt Robert Allenby (Aus) at 23rd hole.






