Martin was denied victory last year by a puncture
World champion Marcus Gronholm was forced to retire at the end of the first day of the Acropolis Rally.
The Finn suffered a fuel pickup problem on the road back to rally headquarters after
the eighth and final stage of the day was cancelled due to spectators on the track.
Ford's Markko Martin, who has yet to win a round of the championship, holds the overnight lead, 4.8 seconds ahead of Peugeot's Harri Rovanpera, with Norway's Petter Solberg in third place for Subaru.
"We expected to have a better lead after this day, to be honest, but it's now only five seconds," said Martin.
"I am pretty confident that if we have good visibility from the car we should be okay for
I had to turn the car where I thought the corners were
Briton Colin McRae, who has won the event for the past three years, moved up to seventh place, 56.8 seconds adrift of Martin.
The Scot had an electrical problem before the second stage and was late arriving at the start, collecting a 50-second penalty.
"It's a lot to make up," said McRae. "It's a tough rally and if you push you could end up
breaking the car. You have got to find a balance."
Martin had to drive for 20km of the fifth stage, the day's longest, with his Focus's bonnet obstructing his view in stifling heat.
"We went into a dip in the road and as we came out of the compression the bonnet flew open, cracking the windscreen and breaking the roof ventilation system," he said.
"I could see no more than 40 metres ahead of us and the cockpit became incredibly hot because there was no air coming in through the ventilator.
It's quite difficult to maintain the flow and concentrate on the road
"I had to turn the car where I thought the corners were. I simply had to react to what I saw at the last minute and I was like a blind man trying to drive a car."
Championship leader Richard Burns was ninth after struggling with gearbox problems on his Peugeot early in the day and acting as 'roadsweeper' by running first on the rough
tracks, one minute 39.7 seconds off the pace.
"It's quite difficult to maintain the flow and concentrate on the road," said the Briton, who has yet to win a race this year but leads Gronholm by two points.
Leading times after Friday's first leg:
Seven stages, eighth stage cancelled
1. Markko Martin (Estonia) Ford one hour 47 minutes 35 seconds
2. Harri Rovanpera (Finland) Peugeot 4.8 seconds behind
3. Petter Solberg (Norway) Subaru 23.9
4. Carlos Sainz (Spain) Citroen 37.9
5. Tommi Makinen (Finland) Subaru 38.2
6. Gilles Panizzi (France) Peugeot 48.2
7. Colin McRae (Britain) Citroen 56.8
8. Didier Auriol (France) Skoda 1:29.7
9. Richard Burns (Britain) Peugeot 1:39.7
10. Manfred Stohl (Austria) Hyundai 2:36.2