Petrofac sank 15.2 percent after warning its 2014 net profit would fall by as much as 11 percent, to between $580 million and $600 million, because of a poor performance from its Integrated Energy Services division.
Analysts said the weak results are being punished more than they would have been in the past, after a powerful rally in 2013 in anticipation of encouraging earnings.
Around two-thirds of companies listed on the pan-European STOXX Europe 600 index have posted first-quarter updates so far. Of those, half have missed consensus earnings forecasts, according to Thomson Reuters StarMine data.
That has left valuations looking full, but a recovering U.S. economy should help pick up the slack. A drop in initial jobless claims on Thursday was the latest signal the U.S. labour market was improving.
The FTSE 100 index trades on a 12-month forward price/earnings ratio of around 13 times, against its 10-year average of about 12 times, Thomson Reuters Datastream shows.
"Individual share prices are likely to react very poorly when you have profits warning like Petrofac ... but the overall market is likely to be driven higher by improving economic momentum out of the U.S," Gerard Lane, equity strategist at Shore Capital, said.
The broader FTSE 100 index closed down 24.68 points, or 0.4 percent, at 6,814.57 points. It had risen to a high of 6,840.37 on Thursday, its highest since late February.
BETTER TO TRAVEL THAN ARRIVE
International Consolidated Airlines Group had the second-biggest decline in the FTSE 100, off 4.8 percent. Investors were locking in profits on the British Airways owner, which has risen around 40 percent in the last 12 months.
IAG reported better-than-expected first-quarter results on Friday. Losses at troubled Spanish carrier Iberia halved, putting it on course for higher annual profits.
"There was a lot of good news in that price. The figures I think were pretty good really - there's nothing of any major issue," Galvan's head of trading Ed Woolfitt said.
While the broader market came under pressure on Friday, it was just some 2 percent away from the all-time high it set in December 1999. Charts suggested it had the potential to set new highs in the near future.
FOREX.com technical analyst Fawad Razaqzada said a close above 6,835, a level where the index is running into resistance, should pave the way for further gains.
"It is just a matter of time before we revisit or surpass the previous record highs," he said.