The Spanish pass-master's 25-yard effort was a saving grace for the Reds who again squandered countless chances in the face of some spirited resistance from ten-man Sunderland.
They had Andy Welsh harshly sent off for kicking out at Luis Garcia, while Steven Gerrard was lucky to escape a second yellow card for a late lunge on Alan Stubbs.
The midweek rumour mill had Djibril Cisse facing the Anfield exit door, but Reds boss Rafa Benitez, who asserted his desire to hold onto the Frenchman in favour of a move for Michael Owen on Friday, rewarded him for some excellent pre-season form with a place in the starting line-up.
However, after Cisse missed a glut of chances many Reds fans may be even more desperate to see the return of the prodigal son, as they edged to victory.
After his side squandered countless opportunities last week in a goalless draw with Middlesbrough, Benitez chose to replace Luis Garcia with Cisse on the right with skipper Gerrard operating behind misfiring Spaniard Fernando Morientes.
For the Black Cats, former Everton stalwart Stubbs made a hasty return to Merseyside to bolster the defence. Former Anfield defender Stephen Wright was ruled out through last week's horror tackle from Darren Ambrose.
After a 15-minute delay due to crowd congestion, a rabid Anfield blew the roof off the place with a rousing welcome for the new European Champions, as the Kop unveiled a mosaic in support of Michael Shields, the Liverpool fan jailed in Bulgaria for an attack on a barman he insists he did not commit.
The Reds almost had the lead within three minutes. A cross from Gerrard evaded everyone including keeper Kelvin Davis as the ball struck the post. Morientes put a fine header just wide from the resulting corner.
Sunderland passed the ball relatively well early on and looked dangerous on the break, while never threatening Jose Reina's goal. Gerrard was booked for a late lunge on Andy Gray as the Black Cats pressed for an unlikely goal.
Meanwhile, Liverpool had further chances through Gerrard and Cisse before they finally had their lead on 24 minutes.
A silly lunge on Bolo Zenden by Carl Robinson was punished immaculately by the imperious Alonso, who curled a 25-yard free-kick past Davis.
Sunderland nearly hit back immediately as Dean Whitehead latched onto Welsh's fine throughball and got in behind Stephen Warnock, but the cross was cleared off the line by Steve Finnan as Gray lurked.
The visitors also had a decent penalty shout when the ball hit Momo Sissoko on the hand, before Whitehead clipped the bar with a cross.
Liverpool reaffirmed their supremacy after the break as a beautifully worked array of one-touch passing almost allowed Morientes in, but Stubbs cleared the danger well.
Gerrard was fortunate to remain on the pitch after a late challenge on Stubbs left him perilously close to a second yellow card. He was then substituted for Luis Garcia - a wise move by Benitez.
A mistake by Gary Breen gave Cisse yet another clean strike on goal, but he volleyed wide with the goal at his mercy – a terrible waste. The Frenchman then had a goal ruled out for offside.
After Gerrard went off Sunderland showed more spirit but little substance as their hard work failed to threaten Reina's goal. Any chance they had of getting back into the game was snuffed out with Welsh's harsh sending-off.
A scrappy win in the end for Liverpool and it won't have gone unnoticed across the country just how much their performance deteriorated when Gerrard left the pitch.
MAN OF THE MATCH: Xabi Alonso (Liverpool) – The classy Spaniard was behind all of Liverpool's best moments and his cool finish spared the Reds' blushes against their ten-man visitors.