Five days after winning his fourth tournament of the season, Dustin Johnson simply carried on where he left off as Rory McIlroy made a stuttering start to his defence of the Dell Technologies Championship.

Johnson overturned a five-shot deficit in the final round before beating Open champion Jordan Spieth in a play-off in the Northern Trust Open on Sunday, the first of four FedEx Cup play-off events.

And the 33-year-old again looked the man to beat at TPC Boston after carding five birdies, an eagle and two bogeys in an opening 66 to claim the lead on five under par.

Starting on the back nine, Johnson holed from 35 feet for birdie on the 10th and just four feet on the 13th, before a careless three-putt on the next.

The former US Open champion bounced back with a birdie on the 15th and hit the pin with his tee shot on the 16th, although he was unable to convert from seven feet for birdie.

A stunning six-iron approach from 220 yards to four feet set up an eagle on the par-five ninth, although a wayward iron off the tee on the first bounced off a cart path and into a hazard, leading to a second bogey of the day.

Undeterred, Johnson promptly birdied the second and fourth and parred his remaining five holes to finish a shot ahead Masters champion Sergio Garcia, his fellow Spaniard Jon Rahm, Australia's Marc Leishman and American Kyle Stanley.

Johnson, who won three tournaments in succession earlier this season before suffering a back injury which forced him to withdraw from the Masters, told PGA Tour Radio: "I drove it well and that's a big key, especially on difficult days with the wind conditions.

"It's blowing pretty good out there. If you can be in the fairway where you can control the spin on the golf ball, it's a big advantage.

"I had one little hiccup on 14, three-putting from about 20 feet - I don't even know what I was thinking. I was so focused on the line I completely forgot about the speed and hit it about 10 feet by.

"But the golf game is in good form right now, I'm feeling good, I've got a lot of confidence and I'm looking forward to the rest of this week."

Garcia looked on course to overtake Johnson when he raced to the turn in 31, but eventually had to settle for a 67 which meant a USD 12,000 donation to the flood relief efforts in Texas.

The world number seven has pledged to donate USD 2,000 for every birdie and USD 5,000 for every eagle he makes during the play-offs.

Defending champion McIlroy, who also won this event in 2012, made an excellent start with birdies on the fifth and sixth, the latter coming from 50 feet.

However, the four-time major winner then three-putted the seventh and amazingly four-putted the 11th from just 11 feet, before dropping another shot on the 15th.

McIlroy at least birdied the par-five 18th to end the day on one over par alongside Spieth, who recovered from playing his first seven holes in three over with a back nine of 34, as well as Scotland's Russell Knox.