Emanuele Canonica stands alone in third place three shots back at minus-13. Jarrod Moseley is one stroke further back at 12-under, while Angel Cabrera and Henrik Nystrom are tied for fifth at minus-11. Cabrera fired a second-round 61, as the field played preferred lies due to the wet conditions.
After heavy rain and thunderstorms washed out play on Friday and caused the tournament to be shortened to 54 holes, play was delayed at the outset on Saturday due to fog. Christopher Hanell and Klas Eriksson finally completed their first rounds early Saturday, before second-round play started.
Poulter, who owned the lead after the first round thanks to a course-record 11-under 61, began his second round on the back nine at Olgiata Golf Club. His round was steady from the beginning as he parred the first six holes. He then stepped to the tee at the par-3 16th and holed out his 4-iron for an ace.
'I hit a 4-iron, straight at the stick and as soon as I hit it I knew it was going to have a reasonable chance,' said Poulter, the 2000 Italian Open champion. 'It pitched seven feet short, checked up and dropped in. It's my third hole-in-one and I've won nothing for any of them.'
He didn't let up from there as he birdied the next and made the turn at 3-under for his round. Around the turn, the Englishman birdied the first to go to minus-4. However, he faltered at the second with a bogey.
Poulter settled down from there with pars on five of his final seven holes. He birdied the fifth and ninth on his way to the clubhouse to get to 16-under. His two round total of 128 was one shot away from the European Tour 36-hole record.
'I've been playing great for six weeks and now it is continuing,' Poulter said. 'It's nice. Steady stuff out there again today. It is always hard to follow a 61 and 5-under is acceptable.'
Lawrie, who opened with a 66, got off to a quick start on the back nine despite trailing Poulter by 10 shots when he teed off. Poulter had an early tee time and had finished at 16-under.
Lawrie, the 1999 British Open champion, opened with birdies on 11 and 12. He later sank birdie putts on 14, 16 and 18 to make the turn at minus-5 and could have done better if not for near misses on 15 and 17.
'I played really nicely again,' said Lawrie. 'I missed chances at a couple of the par-5s, the 15th and 17th but you cant grumble with a 63. Disappointing not to birdie those two holes as I was hitting a little 4-iron into the 15th and a 2-iron into 17th. Two shots dropped you feel but it's a good score.'
On the front nine, Lawrie birdied three consecutive holes starting at the fourth. He closed out his round with a birdie at the par-five ninth.
'It's not great when you stand on the first tee and you are ten behind especially after a good first day but my attitude was really good and I got a good score and gave myself a chance for tomorrow,' said Lawrie. 'I am swinging it well and rolling it well.'
Miles Tunnicliff is alone in seventh place at 10-under par. Gary Orr, Thomas Levet, Anders Hansen and Maarten Lafeber are one stroke further back at minus-9. Mark Mouland, Andrew Marshall, Anthony Wall, Barry Lane and amateur Francesco Molinari are all at 8-under.
Padraig Harrington, who is chasing Retief Goosen for the Order of Merit title, is tied for 34th at minus-5. Goosen is playing in the season-ending Tour Championship on the PGA Tour this weekend.
Defending champion Gregory Havret withdrew after shooting a 1-over 37 on the front side Saturday. He had struggled with an opening-round 75.
The 36-hole cut fell at three-under-par 141.
Full-field scores from the Italian Open