Harlequins, up 28-0 at half-time, ended up clinging on to a 34-26 victory over Cardiff Blues in the Challenge Cup on Sunday.
As a result of their bonus point win Harlequins have secured a home quarter-final.
Chris Robshaw was named man of the match with England assistant coach Steve Borthwick watching on from the stands ahead of the Six Nations.
Rob Buchanan opened the scoring for Harlequins before Jack Clifford, called up by England this month, burst through a hole off the back of a rolling maul to double his side's tally.
Marland Yarde was the next to score as he showed his speed from close range and Harlequins wrapped up the try bonus point before half-time when a clever kick from Nick Evans set up Ross Chisholm for try number four, making it 28-0.
Cardiff Blues showed great spirit however after the break, Cory Allen the first to go over.
Dan Fish did well to finish in the corner before a Nick Evans penalty stemmed the tide momentarily, but Lloyd Williams' solo effort kept the visitors' momentum going.
Fish's second score set up a tense finish but Harlequins clung on, a Ben Botica penalty making sure of the result.
Tries: Buchanan, Clifford, Yarde, Chisholm
Cons: Evans 4
Pens: Evans, Botica
For Cardiff Blues:
Tries: Allen, Fish 2, L Williams
Cons: Patchell 3
Harlequins: 15 Mike Brown, 14 Marland Yarde, 13 George Lowe, 12 Jamie Roberts, 11 Ross Chisholm, 10 Nick Evans, 9 Danny Care, 8 Nick Easter, 7 Jack Clifford, 6 Chris Robshaw, 5 Charlie Matthews, 4 George Merrick, 3 Will Collier, 2 Rob Buchanan, 1 Joe Marler.
Replacements: 16 Dave Ward, 17 Mark Lambert, 18 Kyle Sinckler, 19 Mat Luamanu, 20 Luke Wallace, 21 Karl Dickson, 22 Ben Botica, 23 Charlie Walker.
Cardiff Blues: 15 Dan Fish, 14 Alex Cuthbert, 13 Cory Allen, 12 Rey Lee-Lo, 11 Tom James, 10 Rhys Patchell, 9 Lloyd Williams, 8 Manoa Vosawai, 7 Josh Navidi, 6 Josh Turnbull, 5 James Down, 4 Macauley Cook, 3 Tau Filise, 2 Kristian Dacey, 1 Sam Hobbs.
Replacements: 16 Ethan Lewis, 17 Tom Davies, 18 Dillon Lewis, 19 Jarrad Hoeata, 20 Ellis Jenkins, 21 Tavis Knoyle, 22 Gareth Anscombe, 23 Gavin Evans.
Referee: Andrew Brace (Ireland)
Assistant Referees: Mark Patton (Ireland), Jonathan Peak (Ireland)
TMO: Jude Quinn (Ireland)