Steven Gerrard's free kick and Daniel Sturridge's deflected shot put Liverpool two goals clear by the 48th minute, but the pressure of being a serious challenger for the title for the first time since 2009 showed in the final half-hour.
Ki Sung-yeung's 76th-minute header came amid a dominant spell for the relegation-threatened visitors and Liverpool survived some hair-raising moments in the last minutes to seal a seventh straight league win.
Hope has turned into expectation at Anfield these past few weeks as Liverpool -- the dominant side in England in the late 1970s and 1980s -- revives its glory days to launch a title challenge against all the odds. Its players' loss of composure in the latter stages was telling, and it is set to get even more nervy over the next few weeks with seven games left.
"We have had a wonderful season until now, but there is still a way to go and the message to the supporters is to keep believing," Liverpool manager Brendan Rodgers said. "As the season goes on, we will embrace the pressure and enjoy it."
The victory lifted Liverpool into second place -- two points above Manchester City, which has two games in hand over the sides above them. But this was not as convincing as the Reds' previous six victories, when they scored at least three goals every game to cement their status as the Premier League entertainers.
"The game was set up for a big party, four or five goals," said Sunderland manager Gus Poyet, who added: "My friends in Uruguay didn't send me one text before the game ... they thought we'd be destroyed."
The game certainly looked like it would go that way when Sturridge found the net, via a deflection off Wes Brown, for his 20th goal of the campaign. That ensured two Liverpool players have scored at least 20 times in the same season for the first time in 50 years, when Roger Hunt and Ian St. John were prolific in leading the line for the Reds.
Luis Suarez's current haul stands at 28 goals and although the Uruguay international didn't add to his tally against Sunderland, he played a key role in the opener.
Santiago Vergini escaped with just a yellow card when he hauled down Suarez when last man. Sunderland hadn't escaped, though, as Gerrard curled the resulting free kick in the 39th into the top corner for his ninth goal in 2014.
Relief spread around Anfield but the nerves were to return midway through the second half, when Liverpool sat back and started to get sloppy in possession.
The deficit was halved when Adam Johnson whipped in a corner that crept through a crowded area for fellow substitute Ki to stoop and head in at the far post. And Sunderland should have returned to the north east with a point as John O'Shea headed a gilt-edged chance wide just before injury time.
It's another win chalked up by Liverpool as it seeks a first league title since 1990 and the club's fans are starting to believe again. The way they cheered Liverpool's players into Anfield before the game got Rodgers' heart beating.
"Our game started on the coach on the way in here," Rodgers said. "Any guys who watched Liverpool in the `70s and `80s coming in, it filled me with great pride being the manager of the club as we were driving in."
Liverpool, which is unbeaten in 2014, has home games remaining against City and Chelsea.
"We are in fantastic position," Gerrard said, "but we haven't won anything yet."
In Wednesday's other game, West Ham ended a three-game losing streak as an own-goal by James Chester secured a 2-1 win over 10-man Hull in a match between two mid-table teams.
Hull goalkeeper Allan McGregor was shown a straight red card after charging into Mo Diame midway through the first half and Mark Noble dispatched the resulting penalty to give West Ham the lead. Nikica Jelavic equalized in the 48th.
