Slack defending led to the breakthrough in the 48th minute.
Hesitant defending led to New Zealand's goal, Gregorius squeezing between two players to stab the ball over the line.
That victory owed much to the ferocious intensity with which PSG played, their ability to exploit Barça's vulnerability from set-pieces, and excellent defending led by David Luiz.
The hosts had marginally the better of a breathless first half but were pegged back deep into injury time after sloppy defending led to a penalty.
Defending leads, not chasing them, is what suits the men from Isfahan, and when Cho Byung-kuk, another central defender, headed home a corner kick for Seongnam after 52 minutes, the game looked finished.
Scrum followed scrum, Saracens perhaps aggrieved that Quins' full contingent stayed on the pitch but some fine last-ditch defending, led by Robshaw, Jamie Roberts and the indefatigable Horwill, kept the visitors scoreless.
One sitting MP has a majority of less than 400, with six others defending leads of well under 3,000.
Roscommon turned up the tempo as they went desperately in search of scores, but they ran into solid Tyrone defending led by Padraig Hampsey, Frank Burns and Kieran McGeary.
Dortmund coach Jurgen Klopp said his side faced "football's biggest challenge" in scoring against an Italian side with a lead to defend and in truth, their own poor defending led to them being comfortably picked apart.
Terrible defending led to Taylor's equaliser and a below-par West Brom were booed off for failing to overcome a side two divisions below them at home.
Hingis, the defending champion, led by 6-3, 3-0 when Henin retired with an inflamed left foot.
