Park were pegged back four times before the top-scorer’s boot secured a first away win in the London derby.
The fly half first scored for Park nine minutes into the game, kicking a penalty beneath the posts.
But Tom White drew the hosts level four minutes later with his own kick.
The first try came after 18 minutes, Nick Scott finishing off on the right wing for his first Park score.
Elthamians’ marauding lock, Perry Parker, secured his own inaugural try five minutes later, smashing through two tries.
But Park ended the half in stunning style, substitute Mike Macfarlane finishing off a swift counter-attack which started on Park’s five-metre line with Henry Robinson’s catch.
Try time for Park
The pattern continued in the second half though, Bryan Hotston finding space underneath the posts two minutes in.
Craig Holland, top try scorer last season for Chinnor, gave Park the lead again on 47 minutes as he found space on the left wing.
Elthamians drove over the line eight minutes later through Jared Saunders to draw level for the last time.
Lound comfortably kicked twice in five minutes for the six-point gate.
The second penalty was a result of Ben King’s interception, seeing Elthamians’ No.8 sin-binned.
But the teams were 14-all three minutes later, Dan Laventure making contact with Charlie Dockery in the air.
The last 15 minutes saw the home side battle for a one-point but were missing the final pass, ending with a losing bonus point.
Park will look to make it three opening wins in a row for the first time since 2015 against Canterbury.
The National 2 play-off winners missed out on an astonishing win over Blackheath as they ended 33-34 at the Marine Travel Ground.
Next Saturday will see the Kent side travel to the Rock for the first time in their history.
Stats
Rosslyn Park
Tries: Scott 18, Macfarlane 37, Holland 47
Conversions: Lound 19, 38, 48
Penalties: Lound 9, 58, 63
Sin bins: Laventure 66
Team (15-9/1-8): Henry Robinson; Nick Scott, Henry Cheeseman, Joe Munro, Craig Holland; Greg Lound, Dave Lewis (Jack Gash 63); Paul Doran-Jones (Ali Wade 40), Karl Gibson, Stewart Maguire (Nick Lovell 40); Jonathan Mills, Henry Spencer (Mike Macfarlance 21); Dan Laventure, Arthur Ellis, Hugo Ellis ©
Replacements: Harry Leonard
Attendance: 348
Referee: Simon Harding
HT: 10-17
Star Man: Henry Cheeseman – Rosslyn Park
Warren Muggleton @WMuggleton
images: David E Whittam
September 16, 2019