LONDON (Reuters) - Matches will be played on the middle Sunday at Wimbledon for the first time since 2004 after heavy downpours continued to plague the rain-ravaged tournament on Friday.

With play badly disrupted on Tuesday, Wednesday and again on Friday, meaning three second-round singles matches were still to be completed on day five, organizers have been forced to take advantage of what is usually a rest day.

The middle Sunday was first used in 1991 and again in 1997.

The fixture backlog meant 16 second-round singles matches were still to be completed at the start of play on Friday, but another stop-start day meant not all were completed.

In rain-free years, Friday would mark the first day of third-round matches in both the men's and women's singles competitions.

This year is the 25th anniversary of what was dubbed "People's Sunday" -- when the general public could buy tickets on the day for the showcourts.

In 1991, only 52 of 240 scheduled matches had been completed by Thursday evening.

Earlier, All England Club Chief Executive Richard Lewis said playing on Sunday was "not a scenario we are wishing to repeat in 2016". However, the fickle British summer intervened.

"The All England Club has confirmed that on account of the poor weather experienced to date in the first week, play will take place on Middle Sunday," organizers said in a statement.

"The move has been made in order to reduce the backlog of matches and to allow The Championships to finish as scheduled.

"Tickets will only be available for purchase in advance online on a first-come first-served basis with a limit of two per household. None will be available for sale on the day."

The last time the men's final was completed on the Monday after the tournament's scheduled close was in 2001, when Goran Ivanisevic became the first and only wildcard to win the event.

The retractable roof since fitted over Centre Court virtually rules out a similar rescheduling being necessary in the future.

Wimbledon is the only one of the four grand slams that schedules play on only 13 days. The French Open uses 15 days, while the Australian Open and U.S. Open play on 14 days.

(Reporting by John Stonestreet, editing by Ed Osmond)