So, through four games, Liverpool's conceded seven goals. All seven have come from set plays (if we count Ashley Young's penalty). Zonal marking has been a scapegoat since Benitez came to the club, so it's worth a look at the proportion of goals Liverpool's conceded that have come from set plays over his five seasons.
Two notes before we get to the graphic.
One, yes, I'm counting penalties. It's probably not fair, but I reckon the easiest distinction is goals from open play versus goals that weren't. It also doesn't fundamentally alter the totals. Two, the stats are from my game notes (if I have game notes), or match reports from the official site, BBC, or the Grauniad (depending on who actually described the goal). I might be missing some, but I've double-checked in almost all cases. My memory's admittedly not the best.
Conclusions? Well, those numbers suggest it's the players, not the system. Liverpool was fairly consistent – and fairly good – over Benitez's first three seasons. Then the number surged in '07-08 (although Liverpool conceded far more penalties that season – six – the percentage is still the highest without spot kicks), and stayed "above average" in '08-09.
What's the difference between then and now? First and foremost, Hyypia stopped being a regular starter. He's considered one of the best defenders in Liverpool history for a reason. Second, Liverpool hasn't been helped by Carragher's aging; he still provides some amazing last-ditch tackles, but he's lost a step, especially in the air, and Hyypia was easily his best partner. Liverpool conceded less from set plays in '07-08 after Skrtel arrived, but not few enough.
Those are the only conclusions I can come to. If "zonal marking" was the problem, you'd expect Liverpool to have conceded the most in '04-05, when it was a new system. But it actually "worked" for the first three seasons, only to see the number of set piece goals rise around 2007.
The complete stats:
0-1 Graz (Tokic, corner); 0-1 United (Silvestre, from FK); 1-2 United (Silvestre, corner); 0-1 Olympiakos (Stoltidis, from FK); 0-1 Chelsea (J Cole, from FK); 0-1 Brum (Anderton, corner); 0-1 Boro (Riggott, from FK); 1-1 Villa (Solano FK); 0-1 Olympiakos (Rivaldo FK); 0-1 Charlton (Bartlett, corner); 0-1 Brum (Pandiani pen); 1-1 Chelsea LC (Gerrard OG, from FK); 0-1 Newcastle (Robert FK); 1-1 Pompey (Kamara, corner); 0-1 Arse (Pires FK); 0-1 Milan (Maldini, from FK)
0-1 CSKA Sofia (Iliev, from FK); 0-1 Chelsea (Lampard pen); 0-1 Bolton (Jaidi, from FK); 1-3 Luton (Nichols pen); 0-1 United (Ferdinand, from FK); 0-1 Chelsea (Gallas, corner); 0-1 Benfica (Luisao, from FK); 2-1 Everton (Cahill, corner)
0-1 Sheffield (Hulse, from FK); 0-1 Bolton (Speed FK); 3-1 Reading LC (Bikey, from FK); 4-3 Reading LC (Long, from FK); 0-3 Arsenal (Gallas, corner); 1-2 Galatasaray (Buruk, corner); 1-2 Arsenal LC (Baptista FK); 1-2 Newcastle (Solano pen); 0-1 United (O'Shea, from FK); 3-1 Arsenal (Gallas, corner); 0-1 Milan (Inzaghi, from FK)
1-1 Villa (Barry pen); 1-1 Chelsea (Lampard pen); 0-1 Porto (Lucho pen); 1-1 Reading LC (Convey, corner); 2-2 Reading CC (Halls, corner); 0-1 Everton (Hyppia OG, corner); 1-1 Cardiff (Purse, from FK); 0-1 Reading (Hunt pen); 0-2 Reading (Doyle, from FK); 0-1 United (Tevez, corner); 1-1 Derby (McEveley, from FK); 1-1 Wigan (Bramble, from FK); 1-1 Villa (Harewood, from FK); 1-2 Villa (Aurelio OG, from FK); 0-1 Havant (Pacquette, corner); 0-1 West Ham (Noble pen); 0-1 Boro (Tuncay, from FK); 3-1 Bolton (Cohen, corner); 0-1 Reading (Matejovsky, from FK); 0-2 United (Ronaldo, corner); 0-1 Arsenal CL (Adebayor, corner); 1-1 Arsenal (Bendtner, from FK); 0-2 Brum (Larsson FK); 2-1 Chelsea CL (Lampard pen)
1-1 Crewe LC (O'Connor, corner); 0-2 City (Garrido FK); 1-1 Spurs (Carra OG, corner); 3-1 Blackburn (Santa Cruz, corner); 0-1 PSV (Lazovic, corner); 0-1 Hull (McShane, corner); 2-1 Newcastle (Edgar, corner); 1-1 Everton (Cahill, from FK); 0-1 Everton FA (Lescott, corner); 1-1 Wigan (Mido pen); 1-2 Pompey (Hreidarsson, from FK); 0-1 Boro (Alonso OG, corner); 0-1 United (Ronaldo pen); 1-1 Chelsea CL (Ivanovic, corner); 2-1 Chelsea CL (Ivanovic, corner); 2-2 Chelsea CL2 (Alex FK)