Reading snatched a 1-1 draw at Manchester United while Chelsea trounced second division Norwich City 4-0 to reach the FA Cup quarter-finals on Saturday.
United dominated the fifth round tie and led with midfielder Michael Carrick's strike in first-half stoppage time, only for midfielder Brynjar Gunnarsson to earn Reading a replay at the Madejski Stadium with a 67th minute equaliser.
Arsenal face a replay at Ewood Park after drawing 0-0 with Blackburn Rovers and Middlesbrough will also play again after being held 2-2 by second division West Bromwich Albion. The three replays will be on Feb. 27 and 28.
Watford beat second division Ipswich Town 1-0, while Plymouth Argyle reached Monday's quarter-final draw with a 2-0 win over leaders Derby County in their all-second division tie.
There was a pulsating finish to the day's action at Old Trafford, where both managers made changes to the starting line-ups, United's Alex Ferguson bearing in mind next week's Champions League last-16 game in Lille.
United had plenty of possession but lacked their usual fluidity going forward, taking the lead with a moment of individual skill in Carrick's low, 25-metre shot -- teed up by Cristiano Ronaldo.
Reading, managed by former United winger Steve Coppell, improved after the break and Gunnarsson headed a superb equaliser.
"I think we've got to regret the chances we missed," Ferguson told Sky Sports News.
Coppell, who rested several top players because the team's priority is their first Premier League campaign, said he would continue this policy and play much the same team for the replay.
Praising his team's achievement of drawing twice with United this season, including once in the league, he said: "They (United) are tremendous and for us to be anywhere near them is a great compliment to the players."
DROGBA'S 26TH
Frank Lampard engineered Chelsea's opening goals at Stamford Bridge. When his shot was blocked, Shaun Wright-Phillips scored from the rebound and from his corner after halftime Didier Drogba pounced for his 26th goal of the season.
Andriy Shevchenko was behind the flurry in stoppage time, squaring for Michael Essien to slot home then nodding Chelsea's fourth.
Coach Jose Mourinho told a news conference: "They gave us a very difficult first half and we were a bit lucky to be winning 1-0... 4-0 is a bit heavy for a team who fought like they did."
Arsenal, who beat Bolton Wanderers 3-1 after extra time in Wednesday's fourth round replay, had virtually all the possession at the Emirates Stadium but lacked their usual bite.
Manager Arsene Wenger told BBC Sport: "They tried to stop us from scoring and they did it well. We lacked a bit of spark, we were a bit flat in the speed of our game."
Middlesbrough were twice pegged back by West Brom, with Julio Arca's opener cancelled out by Diomansy Kamara and a Yakubu Aiyegbeni penalty getting the same treatment from Kevin Phillips's equaliser.
Watford, battling relegation from the Premier League, went through with an 88th-minute strike by Damien Francis and helped by a 45th-minute red card for Ipswich midfielder George O'Callaghan.
Fulham host Tottenham Hotspur, while second division Preston North End are at home to Manchester City on Sunday.
(Additional reporting by Clare Lovell and Sonia Oxley)